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IMAGE  EVALUATION 
TEST  TARGET  (MT-3) 


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Photographic 

Sciences 

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23  WIST  MAIN  STRUT 

WCBSTIR.N.Y.  USM 

(71*)  •73-450;* 


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CIHM/ICMH 

Microfiche 

Series. 


CIHJVI/ICMH 
Collection  de 
microfiches. 


Canadian  Institute  for  Historical  Microreproductions  /  Institut  Canadian  de  microraproductionr  historiquas 


Technical  and  Bibliographic  Notes/Notes  techniques  et  bibliographiques 


The  Institute  has  attempted  to  obtain  the  best 
original  copy  available  for  filming.  Features  of  this 
copy  which  may  be  bibliographically  unique, 
which  may  alter  any  of  the  images  in  the 
reproduction,  or  which  may  significantly  change 
the  usual  method  of  filming,  are  checked  below. 


D 


D 


n 


D 


D 


Coloured  covers/ 
Couverture  de  couleur 


I      I    Covers  damaged/ 


Couverture  endommag6e 


Covers  restored  and/or  laminated/ 
Couverture  restaurie  et'ou  pelliculie 


I      I    Cover  title  missing/ 


Le  titre  de  couverture  manque 

Coloured  maps/ 

Cartes  giographiques  en  couleur 

Coloured  ink  (i.e.  other  than  blue  or  black)/ 
Encre  de  couleur  (i.e.  autre  que  bleue  ou  noire) 


r~~1    Coloured  plates  and/or  illustrations/ 


Planches  et/ou  illustrations  en  couleur 

Bound  with  other  material/ 
Reli6  avec  d'autres  documents 

Tight  binding  may  cause  shadows  or  distortion 
along  interior  margin/ 

La  re  liure  serrde  peut  causer  de  I'ombre  ou  de  la 
distortion  le  long  de  la  marge  intirieure 

Blank  leaves  added  during  restoration  may 
appear  within  the  text.  Whenever  possible,  these 
have  been  omitted  from  filming/ 
II  se  peut  que  certaines  pages  blanches  ajoutAes 
lors  d'une  restauration  apparaissent  dans  la  texte, 
mais,  lorsque  cela  6tait  possible,  ces  pages  n'ont 
pas  6t6  fiimies. 

Additional  comments:/ 
Commentaires  suppidmentaires; 


L'Instltut  a  microfilm^  le  meilleur  exemplaire 
qu'll  lui  a  M  possible  de  se  procurer.  Les  details 
de  cet  exemplaire  qui  sont  peut-Atre  uniques  du 
point  de  vue  bibliographique,  qui  peuvent  modifier 
une  image  reproduite,  ou  qui  peuvent  exiger  une 
modification  dans  la  methods  normale  de  filmage 
sont  indiquds  ci-dessous. 


I      I   Coloured  pages/ 


a 


K 


D 


Pages  de  couleur 

Pages  damaged/ 
Pages  endcmmagdes 


□    Pages  restored  and/or  laminated/ 
Pages  restaur6es  et/ou  pelliculies 


Pages  discoloured,  stained  or  foxed/ 
Pages  d6color6es,  tacheties  ou  piqudes 


□    Pages  detached/ 
Pages  ditachdes 


Showthrough/ 
Transparence 


|~n    Quality  of  print  varies/ 


Quality  inigale  de  I'impression 

includes  supplementary  material/ 
Comprend  du  materiel  euppiimentaire 

Only  edition  available/ 
Seule  Edition  disponible 


Pages  wholly  or  partially  obscured  by  errata 
r.t^ps,  tissues,  etc.,  have  been  refilmed  to 
ensure  the  best  possible  image/ 
Les  pages  totalement  ou  partiellement 
obscurcies  par  un  feuillet  d'errata,  une  pelure, 
etc.,  ont  6t6  film^es  A  nouveau  de  faqon  A 
obtonir  la  meilleure  image  possible. 


This  item  is  filmed  at  the  reduction  ratio  checked  below/ 

Ce  document  est  film6  au  taux  de  reduction  indiquA  ci-dessous. 

10X  14X  18X  22X 


J 


12X 


16X 


20X 


26X 


30X 


24X 


28X 


] 


32X 


aire 
details 
ues  du 
t  modifier 
ger  una 
I  filmage 


The  copy  filmed  here  hae  been  reproduced  thanks 
to  the  generosity  of: 

National  Library  of  Canada 


The  images  appearing  here  are  the  best  q  jaiity 
possible  considering  the  condition  and  legibility 
of  the  original  copy  and  in  keeping  with  the 
filming  contract  specifications. 


L'exemplaire  filmA  fut  reproduit  grAce  d  la 
gAn6rosit6  de: 

Bibliothdque  nationale  du  Canada 


Las  images  suivantes  ont  6x6  reproduites  avec  le 
plus  grand  soln,  compte  tenu  de  la  condition  et 
de  la  nettetA  de  rexemplaire  f ilm6,  et  en 
conformity  avec  les  conditions  du  contrat  de 
fiimsge. 


i6as 


Original  copies  in  printed  paper  covers  are  filmed 
beginning  with  the  front  cover  and  ending  on 
the  last  page  with  a  printed  or  illustrated  impres- 
sion, or  the  back  cover  when  appropriate.  All 
other  original  copies  are  filmed  beginning  on  the 
first  page  with  a  printed  or  illustrated  impres- 
sion, and  ending  on  the  last  page  with  a  printed 
or  illustrated  impression. 


Les  exemplaires  orlginaux  dont  la  couverture  en 
papier  est  imprim6e  sont  filmte  en  commenpant 
par  le  premier  plat  et  en  terminant  solt  par  la 
derniire  page  qui  comporte  une  empreinte 
d'imp.esslon  ou  d'illustration,  soit  par  le  second 
plat,  salon  le  cas.  Tous  les  autres  exemplaires 
orlginaux  sont  fiimis  on  commandant  par  la 
premiere  page  qui  comporte  une  empreinte 
d'impression  ou  d'illustration  et  en  terminant  par 
la  darniAre  page  qui  comporte  une  telle 
empreinte. 


The  last  recorded  frame  on  each  microfiche 
shall  contain  the  symbol  — »>  (meaning  "CON- 
TINUED"), or  the  symbol  V  (meaning  "END"), 
whichever  applies. 


Un  des  symboles  suivants  apparaitra  sur  la 
dernlAre  image  de  cheque  microfiche,  selon  le 
cas:  le  symbols  — ►  signlfie  "A  SUIVRE".  le 
symbols  y  signlfie  "FIN". 


ire 


Maps,  plates,  charts,  etc.,  may  be  fHmed  at 
different  reduction  ratios.  Those  too  large  to  be 
entirely  included  in  one  exposure  are  filmed 
beginning  in  the  upper  left  hand  corner,  left  to 
right  and  top  to  bottom,  as  many  frames  as 
required.  The  following  diagrams  illustrate  the 
method: 


Les  cartes,  planches,  tableaux,  etc.,  peuvent  Atre 
film6s  A  des  taux  de  reduction  diffArents. 
Lorsque  le  document  est  trop  grand  pour  Atre 
reproduit  en  un  seul  clichA,  (I  est  fiimA  A  partir 
de  Tangle  supArieur  gauche,  de  gauche  A  droite, 
et  de  haut  en  bas,  en  prenant  le  nombre 
d'images  nAcessaire.  Les  diagrammes  suivants 
illustrent  la  mAthode. 


ly  errata 
Bd  to 

nt 

ne  pelure, 

ipon  A 


H 


1  2  3 


32X 


1 

2 

3 

4 

5 

6 

¥. 


A   SCHOOL   CHEMISTRY 


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SEP  3   0  19 G4 


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■■'VOjvta^^S^ 


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A  SCHOOL  CHEMISTRY 


INTENDED    FOR    USE    IX  Jffr.'fl   SCHOOLS 

AND  IN  ELEMENTMIV  CLASSES 

IN  COLLEGES 


I » 


/ 


HY 


JOHN    VVADDKLL 


B.A.  (Dal.  Coll.),  B.Sc.  (Lond.),  Pn.I).  (IIeidelbkro) 

D.Sc.  (Em.N.) 

^  MEMBER   OF   THE  AMKKICA.V   CHEMICAL   SOCIETY 

FORMERLY   ASSISTANT  TO   THE    PROFESSOR  OF   rHEMISTKY   IN    EDINBURGH 
UNIVERSITY;    LECTURER   IN   CHEMISTRY   IN   THE   SCHOOL 
OF   MININC,    KINGSTON 


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^<^    I  IPP4PY.      %\ 


StP  3   0  1904 


•♦-■n«r-.-'.»T»3->»»'-"  •■ 


THE   MACMILLAN   COMPANY 

LONDON:  MACMILLAN  &  CO.,  Ltd. 
1900 

All  rights  reserved 


211308 


^ 


J^i^^ 


COPYUIOHT,    I'tOO, 

By  the  MACMILLAN  COMPANY. 


J.  S.  Cushinj?  *  C  ).      Borwick  &  Smith 
Norwood  Mags.  I'.S.A. 


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^/^     SEP  3   0  1904  1 

A  o 

'tis  *»»»^^    — »*••  ^ 


PREFACE 

Ax  occasional  visitor  to  the  ordinary  public  lecture  on  chem- 
istry, whose  eyes  have  been  dazzled  by  a  display  of  fireworks, 
regards  the  subject  as  most  interestinj,'  and  fascinating,  and 
supposes  that  the  chemist's  life  is  spent  amid  a  continuous 
round  of  brilliant  pyrotechnics.  The  student,  whetlier  at 
school  or  college,  takes  quite  another  view  of  the  matter,  and 
very  frequently  considers  chemistry  one  of  the  most  difficult 
subjects  of  his  course.  He  meets  a  large  number  of  new  facts 
which  unfortunately  seem  unconnected  with  ordinary  daily 
life.  The  idea  is  soon  formed  that  chemistry  is  a  thing  aj)art, 
that  it  forms  a  realm  by  itself,  presided  over  by  a  special  god 
or  goddess,  —  a  deity,  alas,  difficult  to  appease  and  propitiate, 
the  secrets  of  whose  kingdom  are  most  grudgingly  revealed. 

Not  only  are  new  facts  met  with,  but  new  theories  are 
encountered,  and  the  theories  do  not  seem  to  arise  from  the 
facts.  If  any  connection  is  regarded  as  existing  between  the 
two,  the  theories  are  supposed  to  be  the  more  fundamental, 
tlie  facts  striving,  if  possible,  to  correspond  with  them.  To 
many  young  students  it  would  be  matter  of  surprise  that 
chemistry  does  not  hang  upon  the  atomic  theory,  that  a  num- 
bfci  of  the  most  brilliant  and  epoch-making  dffecoveries  were 
made  without  its  assistance,  that  analyses  were  carried  on  and 
manufactures  engaged  in  before  the  theory  was  enunciated, 
and  that  without  the  experimental  basis  provided  by  research, 
the  atomic  theory  would  be  of  no  more  value  than  the  unfruit- 


VI 


VUKFAVE 


ful  hypotljosis  of  Domocritus.  The  l)<\t,Minior  is  liable  to  con- 
sider tlijit  he  has  made  [,n't'at  advance  wlieii  he  has  learned  to 
call  water  H./),  t]ioii.L(li  the  probability  is  that  he  has  no  idea 
why  the  formula  is  given,  and  has  very  vague  notions  as  to  its 
real  meaning  and  significance. 

The  endeavour  is  made  in  this  little  book  to  help  the  pupil 
in  the  discovery  of  new  facts,  to  enable  him  to  see  their  con- 
ncH'tions,  and  to  show  how  facts  lead  to  theory,  and  theory  aids 
in  investigation  and  in  the  discovery  of  further  facts.  The 
subject  is  i)resented  in  what  seems  to  me  the  correct  per- 
spective, theory  being  subordinated  to  fact. 

The  order  in  which  the  various  topics  are  taken  up  appears 
to  me  to  be  the  most  simple.  Water  is  first  discussed,  as  being 
one  of  the  most  common  substances,  and  one  with  whose  prop- 
erties the  pupil  is  already  somewhat  familiar.  Thereafter 
follows  the  consideration  of  hydrogen  and  oxygen,  the  latter 
leading  up  to  the  study  of  air  and  its  constituents.  Through- 
out the  book  the  arrangement  is  ecjually  simple.  Definitions 
are  brought  in  as  they  are  needed  and  as  they  arise  from 
consideration  of  the  facts  investigated.  No  mention  of  the 
atomic  theory  is  introduced  until  the  study  of  a  large  number 
of  facts  has  afforded  an  intelligible  basis  for  it,  until,  indeed, 
the  pupil  has  in  his  possession  most  of  the  facts  upon  which 
Dalton  founded  the  theory.  He  is  thus  enabled  to  obtain  an 
accurate  view  of  the  real  meaning  of  formulae  and  an  ability 
to  use  them  correctly. 

One  of  the  difficulties  of  many  students  in  the  continued 
pursuit  of  chemistry  after  leaving  school  is  that  they  have  to 
unlearn  a  good  many  things  that  they  have  learned  (or  mis- 
learned)  in  their  early  study.  It  is  hoped  that  the  student  of 
this  book  will  have  no  such  experience,  but  that  he  will  have 
laid  a  thoroughly  solid  foundation  with  no  crumbling  stones 


PUKFACK 


Vll 


nor  untomporod  mortar.  'riioii<^li  tlio  luodorn  theory  of  cUh'- 
trolytic  dissociation  lias  not  Itccn  introduced,  since  I  do  not 
think  it  advisal)h^  in  an  chMuentary  l)ook  of  tliis  cl»aracter,  I 
trust  that  few  statements  will  he  found  at  variance?  with  the 
most  recently  discovered  facts.  I  have  endeavoured  to  make 
any  description  of  industrial  processes  uj)  to  date,  and  not  to 
descril)c  obsolete  processes  as  thou,L,di  actually  employed  !»t  the 
present  day.  As  .an  example,  I  njay  miMition  the  electrolytic 
})r()(luction  of  sodium  which  has  entirely  su})erseded  the  reduc- 
tion of  th(»  carbonate  by  carbon,  and  even  the?  later  process  of 
reduction  of  the  liydroxide  by  iron  and  carbon. 

I  trust  that  the  book  will  not  oidy  }»rove  valuable  to  the 
pupil  taking  up  chemistry  with  a  view  to  further  study  of 
the  subject,  but  that  it  will  be  found  i)reeminently  useful  from 
an  educational  point  of  view.  The  interroj^atory  method  is 
larjjfely  employed;  the  (pu'stions  thou«,di  for  the  most  part 
simple  are  intended  to  stimidate  thout,dit,  Ix'ing  calculated  to 
niake  the  pu}>il  observe  the  imi)ortant  i)henomena,  t»)  see  their 
connections,  and  to  understand  their  full  significance.  Tt  is 
hoi)ed  that  in  this  respect  the  book  will  prove  itself  su])erior 
to  most  of  the  text-books  on  chemistry  written  for  high  school 
and  college  use. 

The  experiments  are  spoken  of  as  though  performed  by  the 
pupil,  but  where  this  is  not  feasible  he  will  be  able  to  follow 
the  experiments  of  the  teacher,  to  whose  judgment  is  left  the 
decision  which  experiments  to  do  himself  and  which  to  leave 
to  the  pupil.  In  fully  e(piipped  schools  the  experiments  may 
all  be  done  by  the  pupil,  but  in  some  schools  it  might  be 
inconvenient  to  provide  many  sets  of  apparatus  for  the  elec- 
trolysis of  water,  for  instance. 

I  have  had  considerable  experience  in  teaching  beginners  in 
chemistry,  both  dull  and  clever,  and  have  found  that  the  diffi- 


Vlll 


PREFACE 


cultips  oncoiinterefl  by  each  class  are  very  similar,  the  difFer- 
oiu'o  bciing  mainly  that  tho  clovpr  ones  can  be  more  easily 
helped  to  overcome  their  difficulties. 

My  experience  as  a  teacher  has  been  widened  by  experience 
as  an  examiner.  Within  two  years  I  examined  over  three 
thousand  papers  in  chemistry,  written  by  i)upils  from  a  great 
numl»er  of  schools,  and  it  was  largely  owing  to  my  experience 
as  an  examiner  that  I  was  led  to  prepare  this  book,  which  I 
trust  will  commend  itself  to  many  teachers  throughout  the 
country. 

While  I  am  indebted  to  a  number  of  friends  for  suggestions 
in  the  treatment  of  particular  points,  1  wish  to  mention  es])e- 
cially  the  help  given  me  by  Mr.  Frank  Rollins,  A.Ii.,  of  the 
I*eter  (looper  High  School  of  New  York  C'ity.  From  the  time 
that  my  project  began  to  take  shape  I  have  l)een  greatly 
helped  by  Mr.  Kollins's  criticisms  and  suggestions,  and  have 
been  encouraged  by  his  kindly  interest  in  the  work. 

J.  W. 

October,  1900. 


e  differ- 
e  easily 

porieiico 
31"  three 
a  great 
perience 
wliiili  I 
out  tlie 

gestions 
3n  esj)e- 
,  of  the 
he  time 
greatly 
1(1  have 

.  W. 


(X)NTKNTS 


;/ 


niAPTKR 
I. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

IX. 

X. 

XI. 

XII. 

XIII. 

XIV. 

XV. 

XVT. 

XVII. 

XVIIT. 

XIX. 

XX. 


Watkk 


oMir 


IIvniuxiKN 

()XY<JKN 

NlTKOdKN  

Cakhon  Dioxidk  am>  Monoxidk 

Action'  of  IIvi)I(<»(Iii.o|{|('   Acim  on  Ai.kams 

Laws  or  Chkmhal  Comhination  axd  tiik  Ai 

TlIKOItY 

Common  Salt  and  Somk  Similau  CoMrorshs 

IIydhociiloimc  Aril) 

The  IIalo(jkns 

XlTKIC    ACII>    AND    THK    OxiDKS    OF    XlTHOWKN 

SiJLPiiru 

TiiK  I'liosi'iiouus  (Juorr  of  Mi.kmf.xts 

Cakhon  

Mktals  ........ 

The  Alkam  Metai.s 

The  Metai.s  of  tiik  Alkaline  Kaijtiis  . 

The  Zinc  (luori'  of  Metals 

The  Thon  (Jk<u'I'  (►f  Mftai.s 

Metals  of  the  Lead  and  of  the  Copper  (irocp 


TAUK 
1 

12 
:v.) 
♦51 


72 


8.-) 
80 
107 
127 
1.-.2 
17.1 
IJKI 


227 


2;'>2 


217 


2.')2 


2KJ 

2U0 


Appendix 
Index    . 


27:J 


275 


IX 


SEP  3  O1904         3 

"^. ■:::;■• ...7...T'_r- :;-*:^' 

SET  OF  CHEMICALs"f()]{   TEN   PITILS 

5  lbs.  Amnion.  Chloiide.  conmicrcial. 

3  '•  "        Nitrate. 

pb.  "        Bromide. 

3  oz.  "         Iodide. 

J  lb.  Antimony  nu'tal. 

^  "  Ar.senic  powdor  metal. 

1  "  Ansinic  Trioxide,  powdered. 

1  "  Barium  Chloride  cryst. 

1   "  Bone-black. 

1  "  Bromine. 

2  lbs.  Carbon  Bisulphide. 

1  11).   Calcium  Chloride,  dry  and  bottle. 

2  lbs.  Calcium  Oxide,  and  bottle. 
I  lb.    Copper  Wire,  naked. 

1  "  ''^       Sulphate  cryst. 

3  lbs.       "       Turnings. 

1  lb.    Ferrous  Sulphate,  commercial. 
3  lbs.       "        Sulphide. 
1  lb.    Gypsum. 
3  oz.   Iodine. 

1  •'     Litmus. 

2  large  sheets  each  red  and  blue  Litmus. 

1  lb.    Lead  Nitrate. 

3  lbs.  Manganese  Dioxide  for  Chlorine. 

2  "     Marble. 
5  *•     Mercury. 

^  lb.    Mercuric  Oxide,  red. 

3  lbs.  Oxalic  Acid. 

1  lb.    l»aratiin. 

2  oz.    IMiosphorus. 

\  "     Potassium,  metal. 

1  lb.  '•  Bromide. 

2  lbs.         "  Chloride. 

xi 


xu 


CHEMISTRY 


\  lb.    Potassium  Iodide. 

1  "    Caustic  Pota.sh  pure  white  sticks. 

2  lbs.  Potassium  Chlorate. 

J  lb.  "  ferrocyanide. 

•JL  lbs.         "  Nitrate  cryst. 

\  lb.    Potass.  Permanganate. 

2  ft.    Platinum  Wire  for  flame  colours. 

1  lb.    Potassium  bichromate. 

\  "    Sodium  metal. 

6  lbs.        "       Carbonate,  dry. 

1  lb.    Caustic  Soda,  puritied,  in  sticks. 

1  "    Sodium  Nitrate. 

J  "  "       Bromide. 

2  oz.         "       Iodide. 

1  lb.         "       Phosphate. 

^  "  "       Diphosphate. 

\  "     Strontium  Chloride. 

6  lbs.  Sulphur,  in  rolls  or  flowers. 

1  lb.  Tin,  granulated,  pure. 

5  lbs.  Zinc,        " 

LIST  OF  CHEMICAL  APPARATUS   REQUIRED   FOR 

EACH   PUPIL 

1  lb.  Glass  Tubing,  assorted  sizes. 

3  Bulb  Tubes. 

1  U  Tube. 

i  doz.  Test-tubes,  4  in.  x  \. 

1  "  '•  6  "    X  \. 

2  Ignition  Tubes  of  hard  glass,  test-tube  shai)e. 

0  ft.  Black  Rubber  Tubing. 

1  Rubber  Cork,  with  two  holes,  to  tit  large  flask. 
6  doz.  Corks,  assorted  sizes. 

8  Cork  Borers. 

1  Flask,  500  cc. 

1      ''      200  cc. 

1      "       Erlenmeyer.  200  cc. 

1      "  "  300  cc. 

1  Deflagrating  Spoon. 

1  Triangular  File,  5  in. 


sets  ' 

cheni 

I 

Mess 

deale 

appa 

T 

that 

11 

terie 

and 


LIST  OF  CHEMICAL   A  PP  A  UMTS 


XIU 


1  Hound  File,  5  in. 

1  Nest  Beakers,  50  cc,  to  400  cc.  approx. 

1  Evaporating  Dish,  3  oz. 

1  ''  '•      (5.J  oz. 

Filter  Paper,  1  package  3  in.,  1  package  4  in. 

1  Funnel  for  each  size  of  paper. 

1  Thistle  Tube,  10  in.;  1  Tube,  15  in. 

1  Retort  Stand,  medium  size,  2  rings  and  1  clamp. 

1  Sand  Bath,  0  in. 

1  Alcohol  Lamp,  6  oz.,  or  Bunsen  Burner. 

Tapers. 

1  Test-tube  Brush. 

1         "         Support. 

1  scjuare  Wire  Gauze,  5  in. 

1  Thermometer,  graduated  to  150°C. 

2  Burettes,  50  cc,  graduated  ^,  with  pinchcock. 

3  Watch  Glasses. 
1  Lime  Tower. 


FOR 


The  price  of  apparatus  and  of  chemicals  may  vary,  but  the  above 
.sets  co.st  approximately  $12.00  for  the  apparatus  and  .'iii25.00  for  the 
chemicals,  exclusive  of  freight. 

I  would  recommend  Messrs.  Eimer  &  Amend  of  New  York  and 
Messrs.  E.  H.  Sargent  &  Co.,  100  Wabash  Avenue,  Chicago,  as  reliable 
dealers,  and  they  will  supply  the  goods  if  asked  for  Waddell's  set  of 
apparatus  or  Waddell's  set  of  chemicals. 

The  set  of  chemicals  for  ten  pupils  may  with  care  suffice  for  double 
that  number. 

If  is  assumed  that  large  apparatus,  such  as  balances  and  electric  bat- 
teries, will  be  in  the  laboratory,  as  also  such  heavy  chemicals  as  acids 
and  alcohol,  and  hence  these  things  are  not  given  in  the  lists. 


Th 

separ 

some 

watei 

failin 

a  litt 

there 

taste ' 

ice   t( 

puttii 

of  do( 

is   col 

siirroi 

a  mixl 

sucli  { 

iiig    i( 

ice  is 

dish,  i 

suffici( 

solid  ] 

fornie( 

SUITOU 

move 


CIIEMlSTliY 


CIIAPTKIl    I 


WATER 


The  Freezing  of  Water.  —  Hxpkuimknt  1.    Into  three 
separate    test-tubes,  or    open    dishes,  such  as  cups,  pour 
some     rain-water,    well- 
water,  and  sea-water  (or, 
failing  that,  water  with 
a  little  salt  in  it).      Is 
there   any  difference  in 
taste  ?    Now,  cause  some 
ice   to    form,    either   by 
putting   the    dishes   out 
of  doors  (if  the  weather 
is    cold   enough)   or    by 
surrounding   them  with 
a  mixture  of  ice  and  salt, 
such  as  is  used  in  mak- 
ing   ice-cream.      If    the 
ice  is  formed  in  an  open 
dish,  it  will  probably  be 
sufficient   to  wash  off  a 
solid  piece  of  it,  but  if  : 
formed    in   a    test-tube, 
surrounded  by  a  freezing  mixture,  it  will  be  best  to  re- 
move the  test-tube  from  the  freezing  mixture  as  soon  as 
»  1 


Fio.  1 


I 


CHEMISTRY 


there  is  a  considerable  quantity  of  ice  formed  in  it,  to 
invert  the  test-tube  over  a  funnel,  as  shown  in  the  figure 
(Fig.  1),  to  allow  the  w^ater  lo  drain  off,  and  then  to  let 
about  one-half  or  two-thirds  of  the  ice  melt  without  being 
disturbed.  Remove  the  ice  to  a  clean  dish;  melt  it,  and 
taste.  How  does  the  taste  compere  with  that  of  the  water 
from  which  the  ice  was  formed  ?  Does  the  salt-water  ice 
taste  salt?  Is  the  water  produced  by  melting  the  ice 
more  or  less  pure  than  the  water  in  which  the  ice  was 
formed  ? 

ExPEKiMKNT  2.  Add  to  some  water  a  grain  or  two  of 
potassium  permanganate  (used  in  Condy's  disinfecting 
fluid).  What  is  the  colour  of  the  water?  Let  ice  be 
formed  as  in  the  first  experiment.  Is  the  ice  coloured  like 
the  water  ?     Does  it  taste  like  the  water  ?  * 

What  is  ont  way  of  getting  moderately  pure  water 
from  an  impure  \/ater? 

The  Distillation  of  Water.  —  A  better  way  of  obtaining 
pure  water  is  to  boil  any  ordinary  water  and  to  cool  the 
steam  that  comes  oft'  from  it  in  such  a  manner  that  the 
water  formed  from  the  steam  miy  be  collected.  This 
process  is  called  distillation,  and  the  water  so  obtained  is 
called  distilled  water. 

*  When  told  to  taste  anything,  always  be  very  careful,  unless  you  are 
perfectly  familiar  with  the  nature  of  the  substance.  It  is  a  good  plan  to 
dip  the  finger  into  the  liquid  and  to  touch  the  finger  to  the  tongue.  In 
case  you  find  the  taste  is  very  slight,  you  may  then  take  more,  unless  you 
are  warned  to  be  careful.  In  the  present  case,  for  instance,  it  will  depend 
on  how  much  permanganate  has  been  used  whether  you  will  be  able  to 
detect  its  taste  in  a  drop  of  the  water,  or  may  need  to  take  a  teaspoonful. 
In  tasting  a  solid,  merely  touch  a  little  crystal  to  the  tongue,  using  iust 
enough  to  distinguish  the  taste.  It  is  always  well  in  your  chemical  experi- 
ments to  avoid  swallowing  anything  until  you  are  quite  sure  that  it  ia 
harmless.    Be  also  very  careful  in  smelling. 


hall 
will 
Hal 


WATER 


8 


I  ill  it,  to 
tlie  figure 
hen  to  let 
lOut  being 
elt  it,  and 
the  water 
-water  ice 
ig  the  ice 
e  ice  was 

or  two  of 
sinfecting 
-et  ice  be 
:>ured  like 

ire   water 

obtaining 

cool  the 

that  the 

d.     This 

tained  is 


ess  you  are 
)od  plan  to 
ongue.     In 

unless  you 
vill  depend 

be  able  to 
jaspoonful. 

using  lust 
leal  exptri- 
i  that  it  is 


Fkj.  2 


ExrERTMENT  3.  Fit  into  a  thin  flask  holding  about 
half  a  litre  (nearly  a  pint)  a  cork  with  a  hole  through 
which  a  long  glass  tube,  bent  as  in  Fig.  2,  i^asses  tightly. 
Half  fill  the  flask  with  salt  water, 
put  in  the  cork,  and  heat  the  flask. 
The  figure  shows  a  piece  of  ai> 
paratus  called  a  retort  stand,  in- 
tended for  holding  vessels  to  be 
heated.  It  also  shows  how  the 
flask  is  held  in  position. 

When  the  water  in  the  flask 
boils,  what  do  you  see  in  the  tube  ? 
When  the  tube  is  all  quite  hot, 
can  you  see  the  steam  in  it  as  well 
as  you  do  what  conies  out  into  the 

air?  Now  put  over  the  tube  a  piece  of  cloth  or  blotting- 
paper  which  has  been  dipped  into  cold  water.  Does  more 
or  less  steam  than  before  come  out  of  the  tube?  What  is 
the  reason  for  the  change?  Catch  in  a  dish  the  liquid 
which  flows  from  the  mouth  of  the  tube.  Such  a  dish  is 
called  a  receiver.  Has  this  liquid  the  same  taste  as  that 
in  the  flask?  Is  it  just  the  same  licjuid?  How  does  the 
taste  compare  with  that  of  the  melted  ice  ? 

This  is  not  a  good  way  to  get  much  distilled  water, 
since  the  blotting-paper  or  clotii  needs  to  be  kept  con- 
stantly wet,  and  the  process  is  neither  neat  nor  con- 
venient. The  great  chemist,  Liebig,*  invented  a  more 
convenient  apparatus  for  cooling  the  steam.  This  appa- 
ratus is  usually  called  a  Liebig's  condenser^  steam  changed 

*  Liebig  is  probably  most  loidehj  known  for  his  Extract  of  Beef,  though 
his  work  in  that  counectiou  was  small  compared  with  the  other  things  he 
did. 


4  C  HEM  I  ST  It  r 

into  water  beiii<^  said  to  be  condensed.  Figure  3  shows 
a  Liebig's  condenser;  the  tube  connected  with  the  flask 
in  which  the  distilhition  takes  phice  is  surrounded  by  a 
jacket  in  Avhich  is  cohl  water.  The  oUl  water  flows  in 
by  a  tube  at  tlie  kiwer  end  and  fl(jws  out  at  the  top 
through  a  tube  to  the  waste.  Whca  a  distilhition  is  tak- 
ing phice,  the  water  flowing  out  is  sliirhtly  heated,  having 
received  heat  from  tlie  steam. 


tha 

esci 

ous 

is  t 

ver 

pare 

liqu 

int 


Fia. 


r---^^^'-^'-^^^^^^^ 


ExPERiMKNT  4.  Partly  fill  a  flask  with  water  con- 
taining a  little  copper  sulphate  (the  blue  vitriol  of 
commerce),  put  in  a  few  pieces  of  broken  glass  or  pottery, 
attach  to  the  condenser,  and  distil.  The  figure  represents 
a  thermometer  in  the  neck  of  the  flask,  wliich  you  may  or 
may  not  introduce  in  your  experiment.  A  liquid,  when 
boiling  in  a  smooth,  glass  vessel,  is  very  liable  to  boil 
unevenly.  For  a  few  seconds  boiling  stops,  and  suddenly 
takes  place  with  violence.     It  is  to  avoid  this  "bumping" 


the 
late 

Y 
said 
pah 
dist 

H 
larg 


WATKR 


3  shows 
lie  flask 
eel  by  a 
flows  ill 
the  toj) 
I  is  tak- 
,  having 


that  the  glass  or  pottery  is  put  in.  Hubbies  of  steam  easily 
escape  from  the  rough  surfaces,  and  the  boiling  is  continu- 
ous. What  is  the  colour  of  the  liquid  in  the  flask  ?  Wliat 
is  the  colour  of  the  liquid  which  distils?  You  may  taste 
very  cautiously  a  little  of  the  liquid  in  the  flask,  and  com- 
pare it  with  the  taste  of  the  distillate  (the  distillate  is  the 
liquid  which  has  been  distilled,  and  -wliicli  you  have  caught 
in  the  receiver).     How  does  the  taste  of  the  distillate  from 


r  con- 
iol  of 
ottery, 
"esents 
nay  or 
when 
o  boil 
Idenly 
ping" 


Fig.  4 


the  copper  sulphate  compare  with  the  taste  of  the  distil- 
late from  the  salt  water  ? 

You  now  know  the  taste  of  distilled  water.  It  is  often 
ST,id  to  be  tasteless,  or  to  have  an  insipid  taste.  Is  it  as 
palatable  as  ordinary  drinking  water  ?  Figure  4  represents 
distillation  as  carried  on  on  the  large  scale  in  the  arts. 

Rain-water  is  a  product  of  nature's  distillation  on  a  very 
large  scale.     It  is  obtained  from  the  evaporation  of  rivers 


6  CHEMISTRY 

and  lakes  and  seas  ;  tlie  vapour  is  cooled  in  the  air  and 
changed  to  the  liquid  form.  Rain-water  usually  contains 
impurities  taken  from  the  air,  but  the  purest  water  in 
nature  is  ''  which  is  obtained  from  rain  or  snow  col- 
lected towaiu  the  end  of  a  long-continued  downfall  at  a 
distance  from  cities.  Why  is  the  water  collected  at  the 
beginning  of  a  heavy  rain  not  so  pure  as  that  collected 
near  the  end  ?  Why  is  the  rain-water  caught  far  out  in  the 
country  purer  than  that  in  cities  ?  What  impurity  would 
probably  be  contained  in  water  caught  in  a  clean  dish  on 
the  deck  of  a  ship  at  sea? 

Ordinary  water  differs  from  distilled  water  because 
ordinary  water  has  taken  something  out  of  the  air  or  out 
of  the  ground.  Rain-water  contains  less  of  other  things 
than  well-water  or  sea-water. 

Solution  in  Water.  —  Experiment  5.  Put  some  sugar 
or  salt  into  water.  What  happens  to  the  solid?  Is  the 
appearance  of  the  water  changed?  Is  its  taste  altered? 
The  sugar  or  salt  is  said  to  bo  dissolved^  and  the  liquid  is 
called  a  solution  of  sugar  or  salt.  Put  some  salt  water 
into  a  porcelain  evaporating  dish  or  crucible  ;  place  it  on 
the  wire  gauze,  and  heat.  Let  the  water  boil  off.  When 
most  of  the  water  is  boiled  away,  heat  carefully,  moving 
the  flame  about  so  that  the  dish  may  not  be  cracked.  What 
is  left  behind  after  the  water  has  been  evaporated  ?  How 
could  you  tell  whether  distilled  water  is  more  or  less  pure 
than  sea- water?  Allow  equal  small  quantities  of  sea- water 
and  of  well-water  to  stand  in  two  dishes  side  by  side  in  a 
warm  place  till  they  are  dried  up.  Which  leaves  the  greater 
amount  of  residue  ? 

Latent  Heat.  —  We  have  seen  that  water  may  exist  in 
three  forms,  as  solid,  as  liquid,  and  as  vapour.     When 


i 


WATER 


lir  and 
ontains 
liter  ill 
ow  col- 
li! at  a 
at  the 
)llected 
t  in  the 
'  wouhl 
dish  on 

because 

or  out 

'  things 

e  sugar 
Is  the 
Itered  ? 
quid  is 
t  water 
it  on 
When 
moving 
What 
How 
ss  pure 
a-water 
de  in  a 
greater 

3xist  in 
When 


the  solid  is  heated  or  the  vapour  cooled,  liquid  water  is 
ohtaiiK'd. 

Exi'EiUMKNT  G.  Half  fill  with  water  a  beaker  (a  glass 
dish  something  like  a  tumbler,  but  thin  so  that  it  can 
be  heated),  and  heat  until  the  water  is  nearly  boiling. 
Remove  the  flame,  i)ut  a  thermometer  *  into  the  water, 
record  the  temperature,  and  lill  up  the  beaker  with  ice, 
whose  temperature  you  have  already  found.  See  whether 
or  not  all  of  tlie  ice  melts.  ( )bserve  the  temperature.  Is 
the  temperature  of  tlie  water,  after  tlie  ice  is  put  in,  half- 
way between  the  temperature  of  the  hot  water  and  that 
of  the  ice?  Repeat  the  experiment,  using  ice-tvater 
instead  of  ice.  Is  the  temperature  after  putting  ice- 
water  into  the  hot  water  higher  or  lower  than  after  put- 
ting ice  into  the  water?  What  does  your  experiment 
sliow  about  the  heat  required  to  melt  ice  ? 

Experiment  7.  Boil  water  in  a  flask  and  lead  the 
steam  through  a  tube  dipping  into  water  which  half  fills 
a  beaker,  having  noted  the  temperature  of  the  steam  and 
of  the  water.  Continue  the  operation  till  the  water  in 
the  beaker  begins  to  boil.  Is  the  beaker  now  full  of 
water  ?  Is  the  weight  of  the  steam  which  heats  the  water 
as  great  as  the  weight  of  the  water  that  has  been  heated 
by  the  steam  ?  How  do  you  explain  the  results  that  you 
have  obtained  ?  What  do  you  now  know  about  the  heat 
required  to  change  a  solid  to  a  liquid  or  a  liquid  to  a 
gas  ?  It  is  usual  to  call  the  heat  required  to  convert  one 
grami'iC  of  ice  at  0°  C.  into  water  at  0°  C.  the  latent  heat 
of  liquefaction  of  ice,  and  the  heat  required  to  convert 
one  gramme  of  water  at  100°  C.  into  steam  at  100**  C.  the 
latent  heat  of  vaporisation  of  water.     The  term  "  latent  " 

*  See  Appendix  on  thermometer. 


8 


CUEMISTUY 


means  hidden.     Tlie  heat  does  not  show  itself  by  causing 
rise  of  temperature. 

Note. —  If  thought  best  this  experiment  may  be  made  more  strictly 
quantitative.  The  steam  thjvt  enters  the  water  must  be  "  diy,"  that 
is,  there  must  be  no  liquid  water  carried  over  with  the  water  vapour. 

Any  water  that  condenses  in 
the  tube  leading  from  the  flask 
should  be  caught  and  not  al- 
lowed to  enter  the  water  in 
the  beaker.  The  form  of  trap 
shown  dX  AB  in  the  figure 
(Fig.  5)  is  a  simple  one. 

Electrolysis  of   Water. 

—  Having  learned  that 
ordinary  water  is  not 
one  simple  substance,  but 
consists  of  pure  water 
with  something  else  in 
it,  it  is  natural  to  ask 
whether  pure  water  is 
itself  a  simple  substance 
or  can  be  broken  up,  that 
is,  separated  into  two  or 
more  otlier  sul)ytances.  If  it  is  a  simple  substance,  it  will 
be  impossible  to  obtain  anything  from  it  but  water,  just 
as  from  gold  nothing  but  gold  can  be  extracted.  It  might 
be  possible  to  add  something  else  to  it,  but  not  to  take 
anything  else  from  it.  If  we  can  break  it  up,  we  show 
that  it  is  a  compound  or  a  mixture. 

Experiment  8.  Put  into  a  dish  some  water  made 
slightly  acid  with  sulphuric  acid.  Fill  two  glass  tubes 
A  and  B  with  this  water  and  invert  in  the  dish.  Bend  a 
strip  of  platinum  so  that  it  can  be  inserted  in  the  tube  A 


Fig.  6 


n^ATER 


0 


causing 

e  strictly 
17,"  that 
r  vapour, 
lenses  in 

the  flask 
tl  not  al- 
water  in 
n  of  ti'ap 
le   figure 

one. 

Water. 

id  that 
is  not 
ice,  but 

water 
else  in 
to  ask 
ater  is 
^stance 
ip,  that 

two  or 

it  will 
er,  just 

might 
to  take 
show 

made 
tubes 
Send  a 
tube  A 


I 


i 


Fkj.  G 


as  in  Fig.  6  and  join  the  platinum  strip  out»'uh'  the  water 

with  a  copper  wire  attacliod  to  the  positive  pole  of  an 

electric  battery.    Connect  the 

tube  B  in  the  same  manner 

with  the  negative  pole  of  the 

battery.*     What  do  you  see 

happen  on  the  surface  of  the 

strips   of    platinum?      Docs 

the    water    continue    to    lill 

the  tubes  A  and  ^?    If  not, 

in  which   tube   does   it   run 

down  the  more  rapidly  ?     Make  sure  that  you  see  with 

which  pole  of  the  battery  the  tube  is  connected. 

Is  what  is  in  the  tubes  A  and  B  air?  In  order  to  find 
out,  remove  the  tubes  without  .allowing  air  to  enter. 
This  may  be  done  by  putting  the  thumb  over  the  mouth 
of  the  tube,  if  the  latter  is  small  enough  ;  or,  if  not,  a 
piece  of  flat  glass,  or  a  bit  of  cardboard.  Turn  the  tubes 
mouth  upward  and  apply  a  burning  match  to  the  mouth 
of  each  tube.  What  happens  when  the  match  is  applied 
to  the  tube  ^?  What  happens  in  tube  B'f  I'lie  sub- 
stances in  the  tubes  A  and  B  that  look  like  air  are  called 
gases.  Does  either  of  the  gases  act  on  the  match  as  air 
would  do  ?  Which  is  least  like  air  ?  The  gas  which  was 
in  greatest  amount  is  called  hydroyen ;  the  other,  oxygen. 

*  No  attempt  is  made  here  to  describe  a  current  of  electricity.  It  is 
assumed  that  the  pupil  understands  that  there  is  an  apparatus  called  an 
electric  battery  ;  that  one  part  of  it  is  called  the  positive  pole,  and 
another  the  negative  pole ;  and  that  if  these  are  joined  by  a  metal  wire  or 
other  conductor  a  current  of  electricity  will  pass.  The  current  may  be 
made  to  pass  through  a  liquid,  provided  it  is  a  conductor  and  the  battery 
is  strong  enough,  or,  to  speak  more  precisely,  has  a  sufficient  electro- 
motive force. 


10 


CUEMI8TRY 


Describe  the  differences  that  you  have  observed  between 
oxygen  and  hydrogen. 

Why  was  sulphuric  acid  added  to  the  water  ?  In  order 
to  find  out,  make  the  experiment  with  distilled  water,  or 
even  with  ordinary  drinking  water.  How  does  the  action 
compare  with  the  former  ?  The  things  that  you  should 
see,  show  that  the  current  of  electricity  does  not  pass  so 
readily  in  pure  water  as  in  water  containing  sulphuric 
acid. 

That  the  hydrogen  and  oxygen  come  from  the  water, 
however,  may  be  shown,  though  j'ou  have  not  been  able 
to  test  it,  by  the  fact  that  after  the  operation  is  all  over 
the  amount  of  sulphuric  acid  in  the  liquid  is  just  the  same 
as  at  the  beginning,  and  that  the  decrease  in  w^eight  of  the 
water  is  exactly  equal  to  the  combined  weight  of  oxygen 
and  hydrogen  produced.  Instead  of  collecting  the  two 
gases  separately  you  may  collect  them  in  one  tube ;  but  if 
you  do  so,  be  extremely  careful  when  you  apply  the  light, 
for  there  will  be  a  very  violent  explosion.  If  you  have 
only  a  test-tube  of  the  mixed  gases  there  is  no  danger  ; 
merely  turn  the  mouth  of  the  tube  away  from  you.  But 
a  larger  vessel  should  either  be  surrounded  by  a  cloth  to 
prevent  tlie  glass  from  flying  if  the  vessel  should  chance 
to  break,  or  some  other  precaution  should  be  taken  to 
avoid  possible  damage.  If  you  dry  the  gases  (as  you  may 
do  by  passing  them  through  a  tube  filled  with  calcium 
chloride)  and  collect  them  in  a  tube  over  mercury,  and 
then  apply  a  match,  you  should,  if  you  look  carefully, 
notice  a  thin  film  of  moisture  on  the  tube.  This  moisture 
is  water.  Is  tiie  volume  of  the  gases  greater  or  less  than 
that  of  the  water  from  which  they  were  obtained,  or  which 
they  combine  to  produce  ? 


J. 

I 


m 

th 


WATER 


11 


between 

[n  order 
^ater,  or 
e  action 
should 
pass  so 
ilphuric 

e  water, 

Jen  able 

all  over 

he  same 

it  of  the 

oxygen 

the  two 

;  but  if 

e  light, 

u  have 

anger ; 

.     But 

loth  to 

chance 

ken  to 

u  may 

alcium 

ry,  and 

•efuUy, 

oisture 

s  than 

which 


i 


When  hydrogen  and  oxygen  are  put  together  the}  are 
said  to  be  mixed^  or  t(^  form  a  mixture  ;  after  the  light  is 
applied  they  combine  to  form  a  compound.  Is  the  mixture 
of  hydrogen  and  oxygen  or  the  compound  formed,  the 
more  like  tlie  gases  wlien  separate  ?  Hydrogen  and  oxy- 
gen have  never  been  decomposed.,  or  broken  up  into  any- 
thing sim})ler,  and  they  are  therefore  called  elements. 

Why  were  you  told  to  join  the  platinum  strips  with  the 
copper  wire  outside  the  water?  In  order  to  answer  this 
question,  try  putting  the  two  copper  wires  themselves 
into  the  tubes,  instead  of  joining  tliem  to  tlie  platinum. 
Have  you  just  the  same  appearance  as  before?  If  not, 
what  is  tlie  difference  ?  Smell  the  hydrogen  which  you 
obtain  tliis  time,  unless  you  have  done  so  already.  A 
process  such  as  that  by  which  hydrogen  and  oxygen  are 
produced  by  a  current  of  electricity  passing  through 
water  is  called  electrolysis.  The  strip  of  platinum  at 
which  the  oxygen  ai)pears,  and  which  is  attached  to  the 
positive  pole  of  the  battery,  is  called  the  positive  electrode, 
or  anode.,  and  the  strip  of  platinum  at  whicli  the  hydrogen 
appears,  and  which  is  attached  to  the  negative  pole  of  the 
battery,  is  called  the  negative  electrode.,  or  cathode. 


CHAPTER   II 


me 
tes 


HYDROGEN 

We  have  found  that  water  can  be  decomposed  by  a 
current  of  electricity,  hydrogen  and  oxygen  being  pro- 
duced. In  chemistry  it  is  very  frequently  the  case  that 
a  compound  is  acted  on  by  a  substance  which  combines 
with  part  of  it  and  sets  the  other  part  free.  This  is  the 
principle  upon  which  lead  and  other  similar  metals  are 
obtained  from  their  ores. 

Decomposition  of  Water  by  Sodium  and  Potassium.  — 
There  are  some  substances  that  act  upon  water,  coir'  in- 
ing  with  part  of  it,  and  setting  free  the  remainder. 
Among  these  are  two  metals  —  potassium  and  sodium. 
These  substances  are  soft  and  lighter  than  water,  and  as 
usually  seen  do  not  look  like  metals,  being  coated  over 
with  a  brownish  crust.  They  are  usually  kept  in  naphtha 
or  some  similar  fluid.  They  can,  however,  be  prepared 
in  a  certain  way,  and  carefully  sealed  up  in  a  glass  tube 
containing  no  air,  so  as  to  present  a  surface  quite  as 
bright  as  silver.  A  method  which  shows  the  silvery  char- 
acter of  the  metal  nearly  as  well  as  the  above  may  be 
tried  with  sodium. 

Experiment  9.  Melt  some  paraflin  wax  in  a  perfectly 
dry  test-tube.  This  may  be  done  by  putting  the  test-tube 
into  hot  water.  Cut  off  a  piece  of  sodium  about  the  size 
of  a  bean,  remove  most  of  the  outside  crust,  making  it 
as  clean  as   you  conveniently  can,  and  drop  it   into  the 

12 


HYDROGEN 


18 


ed  by  a 
ng  pro- 
ase  that 
ombines 
is  is  the 
itals  are 

slum.  — 

coir-  in- 
liainder. 
sodium. 
,  and  as 
ed  over 
laphtha 
repared 
Lss  tube 
uite  as 
ry  char- 
may  be 

erfectly 
!st-tube 
he  size 
king  it 
ito  the 


^■^ 


r? 


r-:- 


') 


melted  paraffin.  Heat  to  boiling  the  water  in  which  the 
test-tube  is  placed.  The  sodium,  if  pure,  will  probably 
be  melted,  but  if  not  remove  the  test-tube  from  the  water, 
dry  it,  and  heat  in  the  flame.  Don't  heat  very  strongly  ; 
you  should  merely  heat  enough  to  melt  the  sodium. 
Keep  it  melted  for  a  little  while  till  the  paraffin  cleans 
off  the  surface  and  you  see  a  silvery  white  glob"le  of 
melted  metal.  Then  allow  to  cool.  If  you  tip  the  test- 
tube  to  one  side  you  may  get  the  sodium  to  solidify 
against  the  glass  and  obtain  a  mirror.  You  should  have 
about  ten  or  twelve  /^ 

times  as  much  par- 
affin as  sodium,  and 
never  allow  the  lat- 
ter to  be  uncovered. 
Experiment  10. 
Throw  a  piece  of 
potassium  about  the 
size  of  a  very  small 
pea  into  a  dish  of 
water.  Does  the 
potassium  sink  in 
the  water  or  does  it 
float  ?  What  colour 
lias  the  flame  ?  Be 
careful  not  to  stand 
too  near  the  dish, 
for  the  potassium 
may  sputter,  and  at 
the  end  there  is  al- 
most certain  to  be  an  explosion,  which  might  be  sufficient 
to  send  out  a  piece  of  the  burning  metal. 


'''ili)' 


0 


J 


IIIII'I'IIM 


IWrrr 


iqe: 


-:Eni\ 


TTTTTT 


|l'll|!'ll||l" 


Fio.  7 


14 


rilEMISTRY 


Repeat  the  experiment  with  sodium,  being  careful  with 
it  also.  What  shape  does  the  sodium  assume  ?  Note 
how  far  it  acts  like  potassium,  and  liow  far  it  differs. 
Is  there  a  flame  ?  Try  the  same  experiment  with  hot 
water.  The  water  should  be,  as  in  Fig.  7,  about  an  inch 
deep,  in  a  beaker  not  less  than  four  inches  deep.  Stand 
off  at  arm's  length  from  the  beaker  when  you  put  in  the 
sodium,  and  it  may  even  be  well  to  turn  away  your  face. 
Place  another  piece  of  sodium  on  a  bit  of  blotting-paper 
or  filter-paper  which  is  floating  on  the  surface  of  cold 
water.  Why  is  there  a  flame  in  some  cases  with  the 
sodium  and  not  in  others  ?  What  is  the  colour  of  the 
flame  ?  Does  sodium  or  potassium  act  the  more  violently 
on  Avater  ? 

Experiment  11.  Wrap  a  small  piece  of  sodium  * 
tightly  in  filter-paper  in  order  not  to  enclose  air  with  the 
sodium,  and  slip  it  quickly,  either  with  the  fingers  or,  bet- 
ter, with  pincers,  into  a  test-tube  full  of  water  and  inverted 
over  a  dish  containing  water.  Is  there  a  flame  this  time, 
when  the  sodium  is  in  the  filter-paper  ?  Notice  the  bubbles 
rising  from  the  sodium.  If  the  piece  of  sodium  is  not  too 
large  (and  it  should  not  be),  these  bubbles  will  cease 
before  the  water  has  all  been  driven  out  of  the  test-tube. 
Remove  the  test-tube  carefull3'  without  allowing  water 
to  escape,  and,  turning  it  mouth  upward,  apply  a  lighted 
match  to  the  gas.  In  what  way  did  you  get  the  same  gas 
before  ?    What  is  the  gas  ? 

Now  examine  the  piece  of  filter-paper.      Is  there  any 

*  Sodium  used  in  this  experiment  must  be  clean,  and  not  coated  with 
the  brown  rind  wliich  forms  on  small  pieces.  Such  small  pieces  should 
not  be  used  at  all,  but  a  freslily  cut  fragment  from  the  inside  of  a  large 
piece,  else  an  explosion  is  very  liable  to  occur. 


•| 


sod 
filte 
iilt( 
Sul 
tha 
litn 
vou 

V 

the 

r 


CI' 


'ik^£Li 


iul  with 
?     Note 

differs, 
with  hot 
an  inch 
Stand 
t  in  the 
jur  face, 
ig-paper 

of  cold 
.vitli  the 
r  of  the 
violently 

lodium  * 
ivith  the 
5  or,  bet- 
inverted 
lis  time, 
bubbles 
not  too 
cease 
st-tube. 
^  water 
lighted 
a  me  gas 

ere  any 

atcd  with 
vs  should 
)f  a  large 


11 


HYDROGEN 


15 


4 


sodium  still  left  ?  Carefully  touch  your  tongue  to  the 
filter-paper.  Also  touch  a  piece  of  red  litmus-paper  to  the 
filter-paper.  To  what  colour  docs  the  red  litmus  change  ? 
Substances  that  have  the  taste  and  the  action  on  litmus 
that  you  have  noticed,  are  called  alkaline.  Test  with 
litmus-paper  a  number  of  the  liquids  in  the  bottles  given 
you,  in  order  to  see  which  are  alkaline.  Put  a  drop  of 
the  liquids  on  the  paper  —  do  not  dip  it  into  the  bottles. 

Pour  the  liquid  remaining  in  tlie  test-tube  in  which  you 
had  the  sodium  into  a  porcelain  evaporating  dish,  and  heat 
till  the  water  is  driven  off.*  Does  what  is  left  behind 
look  like  sodium  ?  Put  a  drop  of  water  on  the  solid,  and 
moisten  your  fingers  with  the  solu^;  n.  What  does  it 
feel  like  ?  You  probably  noticed  tlie  same  feeling  when 
you  touched  tlie  filter-paper. 

We  find  that  we  get  hydrogen  by  tlie  action  of  sodium 
on  water,  and  by  experiments  carefully  carried  out,  it  can 
be  shown  that  the  solid  left  behind  when  all  of  the  water 
into  which  the  sodium  is  put  is  evaporated  weighs  more 
than  the  sodium  that  is  put  in.  It  can  be  shown  that  the 
substance  contains  all  of  the  sodium,  and  that  it  contains 
oxygen  and  some  hydrogen ;  also  that  the  oxygen  and 
hydrogen  combined  with  the  sodium  are  not  in  the  same 
proportions  as  in  water,  but  that  the  hydrogen  set  free 
would  make  up  the  difference.  In  this  or  some  similar 
way  it  can  be  proved  that  the  hydrogen  obtained  by  the 
action  of  sodium  on  water  is  derived  from  the  water  and  not 
from  the  sodium.     The  substance  with  the  soapy  feel  left 

*  If  thore  is  only  a  little  water  left  in  the  test-tube,  it  may  be  necessary 
to  add  part  of  that  in  the  dish.  It  is  better  to  take  ordy  so  much  sodium 
as  to  provide  enough  gas  to  half  lill  the  test-tube,  and  then,  if  the  test-tube 
be  removed  at  once,  nearly  all  of  the  products  of  the  reaction  will  be  in  it. 


16 


CHEMISTRY 


behind  when  the  water  was  evaporated  is  ordinarily  called 
caustic  soda  and  is  used  for  making  soap. 

Decomposition  of  Water  by  Iron.  —  A  number  of  other 
metals,  if  liea*  ^.d  to  a  sufficiently  high  temperature,  also 
decompose  water.  The  very  first  time  that  water  was 
analysed,  that  is,  was  decomposed  into  its  parts,  was  in 
1783,  when  Lavoisier  first  made  the  experiment.  His 
method  was  to  heat  iron  filings  in  a  tube  (he  used  a  gun- 
barrel)  through  which  steam  was  passed.  He  found  that 
the  steam  that  went  into  the  tube  was  partly  used  up  ; 
also,  that  a  gas  came  out  from  the  tube,  and  that  this 
gas  was  the  same  as  had  been  discovered  in  1766  by 
Cavendish  and  named  by  him  inflammable  air.  Lavoisier 
gave  it  the  name  of  hydrogen  (meaning  water  producer). 
Lavoisier  found  that  the  iron  increased  in  weight,  and 
that  the  weight  of  the  hydrogen  produced,  added  to  the 
increase  in  weight  of  the  iron,  was  equal  to  the  weight  of 
the  steam  decomposed.  The  iron  was  changed  into  a 
substance  that  Lavoisier  knew  to  be  obtained  from  iron 
and  oxygen,  and  so  he  proved  that  water  was  made  up 
of  oxygen  and  hydrogen.  When  a  current  of  electricity 
is  passed  through  water,  water  is  analysed,  and  both  the 
products  of  analysis  are  obtained ;  but  it  is  very  seldom 
that  an  analysis  is  made  in  such  a  way  as  to  give  all  the 
parts  of  the  compound  separately,  nor  is  it  necessary. 
Lavoisier's  proof  that  water  consists  of  oxygen  and  hydro- 
gen was  perfectly  satisfactory,  and  it  was  not  till  several 
years  later  that  water  was  electrolysed.  It  must  be  dis- 
tinctly understood,  however,  that  if  Lavoisier  had  not 
known  from  former  experiments  that  the  substance  into 
which  the  iron  was  changed  was  a  compound  of  iron  and 
oxygen,  he  would  not  have  proved  by  the  experiment 


des( 
gen 
Lav 


HYDROGEN 


17 


ly  called         | 

of  other 
lire,  also 
ater  was 
J,  was  in 
lit.  His 
(1  a  gun- 
and  that 
ised  up  ; 
that  this 
1766  by 
Lavoisier 
oducer). 
ght,  and 
ed  to  the 
v^eight  of 
d  into  a 

om  iron 

nade  up 
ectricity 

3oth  the 
seldom 

e  all  the 

cessary. 

d  hydro- 
several 
be  dis- 

lad   not 

nee  into 

ron  and 

)eriment 


described  tliat  water  is  a  compound  of  oxygen  and  hydro- 
gen. Figure  8  shows  a  form  of  apparatus  for  repeating 
Lavoisier's  experiment. 


Fig.  8 


Action  of  Sulphuric  Acid  on  Iron  and  Zinc.  —  Experi- 
ME>'T  12.  Put  into  a  test-tube  a  few  iron  tacks,  cover 
them  with  water,  and  add  a  little  sulpliuric  acid.  Notice 
the  smell  of  the  gas.  Apply  a  light  to  the  mouth  of  the 
test-tube  turned  from  you.  (Test-tubes  should  always  be 
held  with  the  mouth  turned  from  you,  unless  you  are 
perfectly  sure  that  nothing  can  happen  to  cause  the  con- 
tents to  be  projected  from  the  tube.  Serious  accidents 
often  happen  to  the  eyes  and  face  through  neglect  of  this 
rule.)  Does  the  gas  seem  like  either  hydrogen  or  oxy- 
gen ?  Does  the  mixture  of  water  and  sulphuric  acit*  need 
as  high  a  temperature  as  water  alone  in  order  t^  cause 
action  on  the  iron  ? 

If,  when  the  action  has  ceased,  there  is  still  a  consider- 
able quantity  of  iron  in  the  test-tube,  pour  the  liquid 
upon  a  piece  of  filter-paper  fitted  into  a  funnel,  and  in  a 
porcelain  dish  catch  the  liquid  that  passes  through.  The 
process  that  you  have  performed  is  called  filtering^  you 
are  said  to  have  filtered  or  to  have  made  a  filtration^  and 

0 


18 


CHEMISTRY 


I 


liiii! 


tlie  liquid  running  through  the  filter  is  called  a  filtrate.  Is 
the  filtrate  more  or  less  clear  than  the  liquid  before  filtra- 
tion ?  What  is  on  the  filter-paper  ?  Evaporate  the  filtrate 
in  the  porcelain  dish  until  nearly  all  of  the  water  lias  been 
driven  off,  and  a  solid  begins  to  appear  ;  then  allow  to 
cool.  Is  there  more  solid  in  the  basin  wlien  the  li(pud  is 
liot  or  when  it  is  cold  ?  What  does  this  show  you  about 
tlie  comparative  solubility  of  the  substance  in  hot  water 
and  in  cold  ?  What  colour  is  the  solid  ?  It  used  to  be, 
and  sometimes  still  is,  called  green  vitriol,  and  sulphuric 
acid  which  can  be  obtained  from  it  is  called  oil  of  vitriol. 

Experiment  13.  Use  a  few  small  pieces  of  zinc  not 
specially  j)ure,  instead  of  the  iron  tacks.  This  time  also 
smell  the  gas  given  off.  Did  the  hydrogen  obtained  by 
electrolysis  of  water  have  a  smell  ?  If  the  smell  that  you 
noticed  in  any  case  was  due  to  impurity,  is  the  gas  from 
iron  or  from  zinc  the  more  impure  ?  When  hydrogen  is 
made  in  the  laboratory  it  is  usually  made  from  zinc.    Why  ? 

Experiment  14.  Into  a  beaker  containing  about  250 
cubic  centimetres  (half  a  pint)  of  water,  slowly  pour  about 
25  c.c.  of  strong  sulphuric  acid.  When  you  begin  to 
pour,  notice  whether  the  sulphuric  acid  floats  or  sinks, 
or  is  at  once  lost  sight  of.  Is  the  acid  heavier  or  lighter 
than  water  ?  Afterwards  keep  stirring  the  solution  with  a 
glass  rod,  as  you  pour  in  the  acid.  Feel  the  beaker  ;  what 
change  of  temperature  do  you  notice  ?  Sulphuric  acid 
should  be  poured  into  water,  and  not  water  into  sulphuric 
acid.  Would  water  poured  into  sulphuric  acid  mix  with 
it  as  quickly  as  sulphuric  acid  poured  into  water  ?  (iive  a 
reason  for  your  answer.  Why  should  there  be  more  dan- 
ger of  spurting  when  water  is  put  into  sulphuric  acid  than 
wheu  the  acid  is  put  into  water  ? 


on 
fu 
a 

ol 
tin 


HYDROGEN 


19 


trate.    Is 
>ru  filtra- 
le  filtrate 
has  been 
allow  to 
li([uiJ  is 
on  about 
[lot  water 
ed  to  be, 
sulphuric 
f  vitriol, 
zinc  not 
time  also 
tained  by 
.  that  you 
gas  from 
irogen  is 
Why  ? 
jout  250 
3ur  about 
jegin  to 
)r  sinks, 
)r  lighter 
)n  with  a 
r  ;  what 
uric  acid 
ulphuric 
nix  with 
Give  a 
ore  dan- 
cid  than 


Fio.  9 


Experiment  15.  Fit  up  a  flask  as  in  Fig.  9.  Througli 
one  of  the  two  holes  in  the  cork  a  tube  witli  a  little 
funnel  at  tlie  top  (often  called 
a  thistle-tube,  from  the  shape 
of  the  bulb-like  funnel)  passes 
tightly,  reaching  nearly  to  tlie 
bottom  of  the  flask.  Through 
the  other  hole  a  tube,  bent  as  in 
the  flgure,  passes,  also  tightly, 
a  little  way  through  tlie  cork. 
Put  into  tlie  flask  a  number  of 

small  pieces  of  zinc  (say  half    * « 

a   handful);    pour   in  enough      ^^ri^^^^i^ 
of    the    dilute    sulphuric   acid 
that    you    have    prepared,    to 

cover  the  zinc  ;  lit  in  the  cork,  and  see  that  the  liquid 
covers  the  lower  end  of  the  thistle-tube.  If  in  a  minute 
or  so  gas  does  not  come  off  raj.'dly  enough,  pour  a  very 
little  atrong  acid  down  the  thistle-tube  and  shake  the 
flask.  So  soon  as  the  gas  is  coming  off  quickly,  notice 
whether  it  escapes  through  the  thistle-tube.  Put  the  end 
of  the  bent  tube  under  water,  and  see  if  the  gas  comes  out 
of  it.  Place  your  finger  tightly  over  the  end  of  the  bent 
tube  and  notice  the  thistle-tube.  Does  the  liquid  rise  in 
the  thistle-tube  ?  If  it  does  not,  your  cork  or  the  tubes 
do  not  fit  tightly  enough.  Why  should  the  liquid  rise  ? 
What  two  uses  does  the  thistle-tube  serve?  What  would 
happen  if  there  were  no  thistle-tube,  and  the  other  tube 
got  stopped  up  when  the  gas  was  being  produced  rapidly  ? 
Why  is  the  thistle-tiibe  sometimes  called  a  safety  tube  ? 

Experiments  with  Hydrogen.  —  Place  the  end  of  the  bent 
tube  under  water  in  a  dish  (usually  called  a  pneumatic 


20 


CflEMISTIiY 


trough,  because   used  for  collecting  gases,  —  the  Greek 
word  pneuma  meaning  a  gas). 

Fill  a  small  cylinder,  or  a  test-tube,  with  water  in  the 
pneumatic  trough,  and  invert  it.  Place  the  end  of  the 
tube  from  which  the  hydrogen  is  escaping  under  the  mouth 
of  the  cylinder  and  collect  the  gas.  When  the  cylinder  is 
full,  remove  it  and  carefully  apply  a  lighted  match  or 
taper.  If  there  is  an  explosion,  let  the  gas  escape  for  a 
while  longer,  and  try  again,  until  the  gas  burns  quietly. 
Then  collect  several  cylinders  of  hydrogen. 

Place  one  cylinder  mouth  upward  on  the  table,  and 
hold  the  other  mouth  downward  for  a  minute  ;  then  apply 
a  lighted  taper  to  the  mouth  of  each  cylinder.  Hold  a 
cylinder  of  air  mouth  downward,  and  bring  beneath  it  a 
cylinder  containing  liydrogen,  as  in  Fig.  10.     In  a  minute, 

or  somewhat  less,  apply  a  taper 
to  the  mouth  of  each  jar.  Is  hy- 
drogen lighter  or  heavier  than 
air  ?  How  has  your  experiment 
given  you  the  information?* 

Hold  a  cj^lmder  of  hydrogen 
mouth  downward  and  push  a 
lighted  taper  far  up  into  the 
gas.  Does  the  taper  continue 
to  burn  ?  Does  hydrogen  sup- 
port  the  combustion  of  the  taper  ? 
Hydrogen  would  act  with  all  the  ordinary  substances 
that  burn  as  it  does  with  the  taper.  Is  it  a  supporter 
of  combustion? 

*  As  an  amusement  soap-bubbles  may  be  blown.  This  may  be  done 
with  an  ordinary  soap  lather  and  a  clay  tobacco  pipe  ;  but  Newth  recom- 
mends a  soap  solution  made  in  the  following  way  :  10  grammes  of  sodium 


Fig.  10 


I 


I 


UYDIiOaEX 


21 


5  Greek 

p  in  the 
I  of  the 
e  mouth 
Under  is 
latch  or 
pe  for  a 
quietly. 

ible,  and 
en  apply 

Hold  a 
eath  it  i\ 
a  minute, 

a  taper 
.  Is  hy- 
ier  than 
periment 
11?* 
lydrogen 

push  a 
into    the 

continue 

jen  8up- 
le  taper? 
tbstances 

mpporter 


|ay  be  done 

rth  recom- 

of  sodium 


Invert  a  cylinder  over  the  pneumatic  trough  and  let 
out  air  till  the  water  runs  up  two-sevenths  of  the  height. 
Then  place  a  cylinder  of  hydrogen  with  its  mouth  below 
the  first  cylinder  and  introduce  enougli  hydrogen  to  fill  it. 
Your  cylinder  now  contains  a  mixture  of  liydrogcn  and  air 
in  the  proportion  of  2  to  5.  Kemove  the  cylinder  in  the 
ordinary  way  and  apply  a  taper  to  its  mouth.  Hydrogen 
and  air  mixed  in  the  above  proportions  give  a  more  violent 
explosion  than  when  mixed  in  any  other  proportion. 

Gas  has  doubtless  now  ceased  to  come  off  from  the 
generating  flask.  If  there  is  zinc  still  present,  as  there 
probably  is,  add  more  acid.  Does  hydrogen  begin  to  come 
off?  If  so,  is  it  proved  that  hydrogen  comes  from  the 
acid  ?  If  you  mix  sulplmric  acid  and  water,  there  is  no 
hydrogen  evolved ;  but  if  you  add  zinc,  hydrogen  is 
formed.  Does  that  fact  prove  that  hydrogen  comes 
from  the  zinc  ?  If  you  are  told  that  zinc  is  an  element 
and  that  after  the  hydrogen  has  been  made  there  is 
just  as  much  water  in  the  flask  as  there  was  at  the 
beginning  of  the  operation,  what  is  your  conclusion  as  to 
the  source  of  the  hydrogen  ? 

oleate  and  400  c.c.  of  distilled  water  are  placed  in  a  stoppered  bottle  and 
allowed  to  stand,  without  warming,  till  the  oleate  is  dissolved.  100  c.c. 
of  pure  glycerine  is  then  added,  and  the  mixture,  after  being  well  shaken, 
is  allowed  to  stand  in  the  dark  for  a  few  days.  The  clear  solution  is 
then  carefully  decanted  into  a  second  stoppered  bottle  and  one  drop  of 
strong  ammonia  solution  added.  If  kept  in  the  dark  and  not  exposed  to 
the  air,  this  solution  may  be  preserved  for  years. 

The  hydrogen  may  be  supplied  by  the  generating  flask  if  passed 
through  a  tube  10  centimetres  long  containing  cotton  wool,  and  the 
bubbles  are  best  made  by  using  a  thistle-tube  instead  of  the  tobacco  pipe. 
As  'oon  as  the  bubble  begins  to  form,  turn  it  upward,  and  when  it  is 
almost  rvady  to  leave  the  thistle-tube  bulb,  give  the  latter  a  slight  jerk  so 
as  to  detach  the  bubble  easily. 


22 


CHEMISTRY 


If  the  hydrogen  is  coining  off  pretty  rapidly,  collect  a 
small  cylinder  full  to  make  sure  that  the  gas  will  hurn 
quietly.  Remove  the  delivery  tuhe  from  the  water  and 
attach  to  it,  by  a  piece  of  rubber  tubing,  a  glass  tube  whose 
farther  end  is  drawn  out  so  as  to  form  a  narrow  opening 
or  jet.  Clamp  this  tube  in  an  almost  upright  position ; 
wrap  the  flask  in  a  cloth  and  light  the  gas  as  it  escapes 
from  the  jet.  What  is  the  colour  of  the  flame  ?  Put  a 
piece  of  fine  iron  wire  into  the  flame.  Is  the  flame  more 
or  less  hot  than  a  candle,  lamp,  or  gas  flame?     Does  it 

give  more  or  less  light  ?  Try 
wire  or  thin  shavings  of  other 
metals  in  the  same  flame.  Do 
you  now  see  why  the  tube 
was  not  placed  vertically  ? 

For  the  next  experiment 
place  the  tube  vertically. 
Put  down  over  the  burning 
jet  a  tube  open  at  l)oth  ends, 
as  shown  in  Fig.  11.  You 
should  get  a  musical  note, 
but  it  may  be  that  the  tube 
is  not  the  right  size  in  pro- 
portion to  the  flame,  in  which 
case  there  will  be  no  sound. 
Try  tubes  of  different  lengths 
-  and  different  diameters,  and 
see  how  the  note  varies.  The 
note  produced  is  really  the  sound  of  a  series  of  explosions, 
and  the  pitch  of  the  note  depends  upon  the  rapidity  with 
which  these  explosions  take  place ;  the  more  frequent  the 
explosions,  the  higher  the  note. 


Fju.  11 


iiruiiOGKy 


28 


oUecl  a 
11  burn 
ter  and 
e  whose 
opening 
osition ; 

escapes 

Tut  a 

lie  more 

Does  it 
t?  Try 
of  other 
me.  Do 
lie    tube 

uilly  ? 
eriment 

rtically. 
burning 
ih  ends, 
L.      You 
al    note, 
he  tube 
in  pro- 
n  which 
sound, 
lengths 
ers,  and 
s.     The 
Iplosions, 
ity  witli 
ent  the 


P. 


4 


Fig.  12 


I 


Phice  over  the  jet  a  retort  fitted  up  as  shown  in  Tig.  12. 
The  bent  tube  reaching  nearly  to  the  bottom  of  the  retort 
is  to  serve  as  a  draught.  What  do 
you  see  in  the  retort  after  the  jet 
has  been  burning  a  little  while? 
If  the  retort  gets  so  hot  that  you 
see  steain  escai)ing  into  the  air, 
through  the  small  tube,  cool  the  re- 
tort by  i)utting  over  it  a  piece  of 
L'loth  dipi)ed  into  cold  water.  After 
half  an  hour  or  so  you  will  jirobably 
have  enough  liquid  to  experiment 
with.*  What  does  it  taste  like? 
Pour  the  liquid  into  a  test-tube  and 
put  in  a  thermometer.  Then  place 
the  test-tube  in  a  mixture  of  snow  or  ice  and  salt.  So 
soon  as  the  liquid  in  the  test-tube  begins  to  freeze,  look 
at  the  thermometer.  Stir  the  liquid  with  the  tliermometer 
to  make  sure  that  it  is  the  same  teni[)erature  through- 
out. What  is  the  temperature  ?  Take  out  the  ther- 
mometer and  keep  the  test-tube  and  liquid.  Now  put 
the  thermometer  into  another  test-tube  containing  dis- 
tilled water,  and  freeze  the  water.  What  is  its  tempera- 
ture of  freezing  ? 

Heat  the  liquid  in  the  tirst  test-tube  until  it  boils  and 
hold  the  thermometer  in  the  vapour.  What  is  its  tem- 
perature ?  Do  the  same  with  distilled  water.  What  is  its 
temperature  ?     AVhat   do  you  conclude  the  liquid  to  be, 

*  It  may  be  convenient  for  all  the  members  of  the  class  to  pour  the 
liquid  obtained  into  one  test-tube  so  that  there  will  be  sufficient  for  the 
tests.  If  It  Is  thought  advisable,  the  jinn  may  be  dried  before  burning  it, 
though  that  seems  an  unnecessary  retinement. 


24 


CHEMISTRY 


which  you  got  by  burning  hydrogen  in  air  ?  What  must 
the  air  contain,  since  hydrogen  burning  in  it  gives  this 
liquid  ? 

Experiment  16.  Grind  up  some  red  hematite  and  see 
whether  it  is  attracted  by  a  magnet.  Put  it  into  a  glass 
tube,  open  at  each  end.  Through  a  cork  at  one  end  pass 
a  tube  which  is  connected  with  a  hydrogen  apparatus. 
To  the  other  end  of  the  tube  containing  the  hematite 
attach  a  bulb  tube  or  some  sort  of  apparatus  for  collect- 
ing the  vapours   produced  by  the  reaction.     The  figure 

(Fig.  13)  represents  a  suita- 
ble arrangement.  After  air 
has  been  driven  out  of  the 
apparatus,  heat  the  tube  con- 
taining hematite.  What  do 
you  see  coming  out  from  the 
tube  ?  Decide  whether  or 
not  the  liquid  which  con- 
denses in  the  bulb  tube  is 
water.  Allow  the  tube  with 
the  hematite  to  cool.  What 
colour  hns  the  powder  now?  Is  it  attracted  by  the  mag- 
net ?  What  two  things  are  there  in  red  hematite  ?  Is 
red  hematite  a  mixture  or  a  compound  of  these  two 
substances  ? 

The  composition  of  water  may  be  determined  either  by 
analysis  —  that  is,  breaking  it  up  into  its  components  —  or 
by  synthesis  —  that  is,  producing  it  by  the  union  of  these 
components.  In  what  experiments  did  you  analyse  water, 
and  in  what  experiments  did  you  synthesise  it  ? 

Now  filter  the  liquid  in  the  flask,  evaporate  the  filtrate 
in  a  porcelain  dish  until  a  solid  begins  to  form,  and  allow 


Fia.  13 


I 


HYDROGEN 


25 


Lt  must 
es  this 

and  see 

a  glass 
nd  pass 
)aratus. 
lematite 

collect- 
e  figure 
J  a  suita- 
Vfter  air 
t  of  the 
tube  con- 
What  do 
|from  the 
lether  or 

ich  con- 
tube  is 

ube  with 
What 

the  mag- 

ite  ?     Is 

liese   two 

3ither  by 

tnts  —  or 

of  these 

|se  water, 

filtrate 
Ind  allow 


I 


to  cool.  What  is  the  colour  and  shape  of  the  solid  crys- 
tals ?  These  crystals  contain  the  zinc  that  was  dissolved, 
along  with  a  part  of  the  sulphuric  acid  used.  Sulphuric 
acid  was  divided  into  two  parts  —  hydrogen,  which  ap- 
peared as  a  gas,  and  another  part  which  united  with  the 
zinc  to  form  white  vitriol^  or,  as  the  chemist  usually  calls 
it,  zinc  sulphate. 

If  you  had  weighed  the  zinc  and  weighed  the  strong 
sulphuric  acid  (not  the  dilute  acid),  you  would  have  found 
that  a  little  more  than  60  grammes  of  zinc  were  dis- 
solved by  100  grammes  of  acid.  Why  was  the  sulphuric 
acid  diluted  (mixed  with  water)  before  being  put  upon 
the  zinc  ?  In  order  to  find  out,  put  some  zinc  into  a  test- 
tube  and  pour  in  a  little  strong  sulphuric  acid.  Does 
strong  acid  act  more  or  less  rapidly  than  dilute  ? 

Statement  regarding  the  Occurrence ,  Preparation,  and 
Properties  of  Hydrogen.  —  As  it  is  impossible  for  us  to 
create  anything,  any  substance  that  we  work  with  must 
either  be  found  ready  made  in  nature,  or  must  be  made 
from  something  else  that  is  found  in  nature.  Only  a  few 
of  the  elements  are  found  ready  made  ;  most  of  them  have 
to  be  separated  from  compounds.  Books  of  chemistry 
very  frequently  describe  an  element  under  three  heads  — 
its  occurrence  in  nature,  its  preparation,  and  its  proper- 
ties. You  should  never  be  satisfied  when  you  are  study- 
ing a  chemical  substance  until  you  have  pretty  clear  ideas 
on  these  three  points.  Since  hydrogen  burns  in  air  you 
would  naturally  not  expect  to  find  any  large  quantity  in 
the  atmosj^here.  As  some  of  the  hydrogen  that  you  made 
escaped  into  the  air  without  you  seeing  it  burn,  it  is  just 
possible  that  a  little  might  exist  in  the  air  unburned, 
and   lately  an    investigator    claims   to   have    found   one 


26 


CHEMISTRY 


part  of  hydrogen  by  volume,  in  about  100,000  parts  of 
air. 

You  have  found  that  hydrogen  exists  in  water.  One- 
ninth  of  the  weight  of  water  is  composed  of  hydrogen, 
which  also  exists  in  all  vegetable  and  animal  tissues. 

You  know  several  ways  in  which  liydrogen  is  prepared  ; 
what  are  they  ? 

You  have  found  out  many  of  the  properties  of  hydro- 
gen. The  properties  of  a  substance  are  usually  'Mvided 
into  physical  and  chemical.  Suppose  we  take  the  physical 
properties  first. 

What  is  the  j)hysical  state  of  hydrogen,  solid,  liquid,  or 
gaseous  ?  What  is  its  colour  ?  smell  ?  taste  ?  What  is  its 
density  ?  To  all  of  these  questions  you  can  give  at  least 
partial  answers. 

Though  hydrogen  is  a  gas  at  ordinary  temperatures,  it 
would  become  liquid  if  made  cold  enough.  There  is  such 
difficulty,  however,  in  lowering  the  temperature  sufficiently 
that  it  was  not  liquefied,  at  all  events  in  any  appreciable 
quantity,  till  1898.  Liquid  hydrogen  boils  at  -  238°  C. 
and  freezes  at  —  256°  C.  Hydrogen  is  very  sparingly 
soluble  in  water.  At  0°  C.  100  volumes  of  water  can  dis- 
solve 2  volumes  of  lij-drogen.  Usually  gases  that  are 
difficult  to  condense  are  sparingly  soluble. 

The  gas  liydrogen  is  the  lightest  substance  known,  being 
less  than  one-fourteenth  as  heavy  as  air.  It  has  been  used 
for  balloons  on  that  account,  but  coal-gas  is  more  suitable, 
being  cheaper  and  not  so  liable  to  leak  from  the  balloon. 

Pure  liydrogen  is  colourless,  odourless,  and  tasteless.  It 
is  not  poisonous  w'  •  n  perfectly  pure,  but  hydrogen  from 
zinc  may  contain  a  little  arsenic,  because  the  zinc,  unless 
specially  purified,  is  liable  to  contain  arsenic,  while  hydro- 


HYDIiOGES 


27 


ar 


ts  of 


One- 
irogen, 
s. 
spared  ; 

hydro- 
^^ivided 
physical 

quid,  or 

uit  is  its 

ut  least 

itures,  it 
3  is  such 
hci'iitly 
) reel  able 

238°  C. 
Daringly 

can  dis- 
that   are 


I 


I 


gen  from  iron  has  very  disagreeable  impurities.  Though 
hydrogen  is  not  poisonous,  one  cannot  live  in  an  atmosphere 
of  hydrogen  any  more  than  in  water,  for  oxygen  is  neces- 
sary to  supi)ort  life.  Let  us  now  consider  the  chemical 
properties  of  hydrogen.  You  liave  seen  the  principal  one, 
namely,  its  great  allinity  for  oxygen,  with  which  it  com- 
l)ines,  producing  great  heat,  always  a  sign  of  vigorous 
action.  More  heat  is  produced  by  the  union  of  hydrogviu 
and  oxygen  than  by  the  same  weight  of  any  other  two 
substances.  The  heat  produced  by  the  union  of  2  grammes 
of  hydrogen  with  16  grammes  of  oxygen  in  the  formation 
of  18  grammes  of  Avater  is  sufficient  to  heat  from  0°  C.  to 
1°  C.  about  68,400  grammes  of  water,  or  nearly  four  thou- 
sand times  its  own  weiglit. 

To  change  ice  into  water  requires  considerable  lieat ;  to 
change  water  into  steam  requires  a  greater  amount  of 
heat ;  to  change  steam  into  the  gases  hydrogen  and  oxygen 
requires  a  stil)  greater  amount  of  heat. 

It  requires  exactly  the  same  amount  of  heat  to  decom- 
pose water  into  iU  constituents  as  is  produced  by  their 
combination.  When  water  is  decom])osed  by  a  current  of 
electricity  heat  is  practically  used  up,  for  the  same  current 
K         miglit  have  been  employed  in  lieating  an  electric  stove. 


|n,  being 
ien  used 
suitable, 
lalloon. 
lless.  It 
len  from 
',  unless 
hydro- 


CHAPTER   III 


OXYGEN 


We  have  seen  tluxt  wlien  wpter  is  electrolysed  oxygen 
as  well  as  hydrogen  is  produced,  and  a  good  deal  of 
oxyge:^  is  now  made  in  this  way  ;  but  in  laboratories  not 
supplied  with  electrical  power  other  methods  are  used. 

We  saw  that  hydrogen  can  be  obtained  from  water  by 
the  action  of  substances  which  take  away  oxygen,  and  it 
might  be  possible  to  produce  oxygen  from  water  by  the 
action  of  something  which  would  take  away  the  hydrogen. 
There  is  no  eotivenient  substance  for  doing  this,  however. 

If  steam  is  heated  to  a  sufficiently  high  temperature  it 
is  decomposed  into  oxygen  and  hydrogen,  but  it  is  not 
eas)/  to  separate  the  two  gases,  though  it  is  not  impossible 
to  do  so. 

We  found  that  oxygen  exists  in  the  air,  but  in  this  case 
also  it  is  dilhcult  to  separate  the  other  constituents  which 
are  with  it  in  the  atmosphere.  . 

Oxygen  obtained  from  Compounds  by  Heat.  —  There  are 
some  substances  containing  oxygen  which  decompose  on 
being  heated,  yielding  oxygen  gas.  In  1772  the  Swedish 
chemist  Scheele  obtained  it  by  heating  nitre,  a  substance 
which  is  often  called  saltpetre,  and  which  chemists  now 
call  potassium  nitrate.  Scheele  named  the  gas  "fire  air," 
because  of  the  great  readiness  with  which  many  substances 
burn  in  it.  The  name  oxygen  was  not  given  till  some 
time  afterward. 

28 


U 


OAT^'^A' 


29 


oxygen 

leal   of 

ies  not 

sed. 

ater  by 
and  it 
by  the 

Irogen. 

3wever. 

iture  it 
is  not 
ossible 

his  case 
which 

lere  are 
)ose  on 
fwedish 
Ibstance 

its  now 
\vf,  air," 
^stances 
11  some 


» 


In  1774  an  Englishman,  Priestley,  not  knowing  of 
Scheele's  work,  discovered  the  gas  by  lieating  red  lead,  a 
substance  used  in  the  manufacture  of  some  red  paints. 
Priestley  later  on  used  "•  red  precipitate  "  or  "  calcined 
mercury  "  as  a  source  from  which  to  obtain  tlie  gas. 

Experiment  17.  In  a  small  dry  test-tube  heat  a  little 
calcined  mercury  (called  now  mercuric;  oxide).  To  what 
colour  does  the  mercuric  oxide  change  when  first  heated  ? 
After  a  minute  or  two  examine  the  upper  part  of  the  tube. 
What  do  you  sCv.  ?  Put  into  the  mouth  of  the  test-tube  a 
glowing  match,  or  pine  splinter.  What  hai)pens  ?  With 
a  splinter  of  wood  or  an  iron  wire  gather  together  into  a 
globule  the  substance  in  the  upper  part  of  the  test-tube. 
What  is  the  substance  ?  What  two  substances  are  in  cal- 
cined mercury.  You  now  see  wdiy  the  name  mercuric 
oxide  is  given  to  the  substancCo  What  two  substances 
are  in  black  oxide  of  manganese.  Black  oxide  of  manga- 
nese is  a  solid  which,  if  heated  strongly  enough,  will  also 
give  oxygen,  red  oxide  of  manganese  being  left  behind. 
Does  the  black  or  the  red  oxide  of  manganese  contain  the 
more  oxygen  ?  The  black  oxide  of  manganese  needs  to 
be  heated  more  strongly  than  mercuric  oxide,  in  order  to 
yield  oxygen. 

Experiment  18.  Heat  in  a  test-tube  a  little  potassium 
chlorate  (called  by  druggists  chlorate  of  potash  and  sold 
in  the  form  of  crystals  or  as  tablets  for  sore  throat). 
After  the  solid  is  melted,  watch  carefully  to  see  whether 
gas  comes  off  immediately  or  whether  the  substance  needs 
to  be  heated  more  strongly.  After  the  gas  has  come  off 
for  a  little  time,  test  it  Avith  a  glowing  match.  What  is 
the  gas  ?  Now  drop  a  little  powdered  black  oxidf  of 
manganese  into  the  test-tube,  taking  care,  as  always,  that 


30 


CHEMISTRY 


the  mouth  of  the  tube  is  turued  from  you.     Do  you  see 
any  difference  ?     If  so,  what  ? 

Experiments  with  Oxygen.  —  Experiment  19.  Mix 
about  20  grammes  of  potassium  chlorate,  wliich  you  weigh 
roughly,  with  about  one-quarter  its  weight  of  black  oxide 
of  manganese  (manganese  dioxide).  Put  the  mixture  into 
a  small  retort  or  large  test-tube  and  fit  up  in  such  a  way 


Juid 


Fig.  14 


that  you  can  collect  over  water  the  gas  which  is  produced 
when  you  heat  the  mixture.  Figure  14  shows  a  retort 
and  a  method  which  may  be  employed.  Collect  a  number 
of  cylinders  of  the  gas.  When  you  have  finished  collect- 
ing the  oxygen,  take  the  delivery  tube  out  of  the  water  or 
open  the  retort  or  test-tube  in  some  way.  Wlfy  do  you  do 
this?  Does  a  gas  occupy  more  volume  when  hot  or  wlen 
cold? 


OXYGEy 


31 


ou  see 

.    Mix 

L  weigh 
i  oxide 
ire  into 
I  a  way 


rocluced 

a  retort 

number 

collect- 

kvatei'  or 

you  do 

lor  wleii 


Into  one  cylinder  *  pour  a  little  lime-water  and  shake  it 
up  in  the  cylinder.  Does  the  oxygen  apparently  make 
any  change  in  the  lime-water?  Now  heat  a  piece  of  cliar- 
coal  till  it  glows  and  introduce  it  into  the  cylinder,  kccj)- 
ing  the  mouth  of  the  cylinder  covered  as  much  as  i)ossil)k'. 
Does  the  cliarcoal  glow  more  or  less  brightly  ?  Does  it 
produce  a  flame?  After  the  charcoal  has  been  in  a  minute 
or  two,  take  it  out  and  shake  up  the  lime-water  once  more. 
What  change  do  you  notice  in  the  lime-water  ? 

Light  a  candle  and  when  it  is  burning  properly,  notice 
the  size  of  the  flame.  Blow  it  out  and  while  the  wick  is 
still  red,  introduce  it  into  a  cylinder  of  oxygen.  What 
happens  ?  Is  the  flame  of  the  candle  bu/ning  in  oxygen 
larger  or  smaller  than  that  of  the  candle  burning  in  air  ? 
Is  it  more  or  less  bright  ?  Cover  the  cylinder  while  the 
candle  is  burning,  so  that  no  air  can  enter.  What  change 
do  you  notice  after  a  while  in  the  flame  of  the  candle  ? 
Wlien  the  candle  goes  out,  remove  it  from  the  cylinder 
{•nd  introduce  some  lime-water.  How  is  the  lime-water 
affected  ?  Have  you  any  reason  for  suspecting  ^hat  there 
IS  the  same  substance  in  the  candle  that  there  was  in  tlie 
charcoal  ?  Has  3'our  experiment  given  you  a  complete 
proof  ?  Did  the  fact  that  potassium  and  sodium  decom- 
posed water  prove  these  two  substances  identical? 

Heat  some  sulphur  in  a  deflagrating  spoon  (a  deflagnit- 
ing  spoon  is  like  a  small  ladle  and  is  called  a  de flag  rat  uui 

*  The  glpss  jars  used  for  preserving  fruit  are  very  good  vessels  for  con- 
taining gases,  as  they  may  be  closed  air  tight.  In  cases  in  the  text  where 
cylinders  are  spoken  of  for  collecting  and  preserving  gases,  these  vessels 
may  be  employed  with  advantage,  provided  small  enough  ones  can  be 
obtained.  Common  wide-mouthed  bottles  holding  two  or  three  ounces 
or  from  seventy-five  to  one  hundred  cubic  centimetres  may  be  used  in 
most  cases. 


i 


32 


CUEMISTltY 


spoon  because  ordinarily  employed  to  hold  substances  that 
are  to  be  burned).  Wlien  the  sulphur  begins  to  burn, 
notice  the  smell  of  the  fumes  and  then  introduce  the  burn- 
ing sulphur  into  a  cylinder  of  oxygen.  How  does  the 
flame  compare  with  that  in  the  air  ?  When  the  sulphur 
ceases  to  burn,  put  a  little  water  into  the  cylinder,  and 
shake.  Is  the  smell  of  the  gas  in  the  cylinder  or  of 
the  solution  in  water  similar  to,  or  different  from,  what 
was  obtained  in  air  ?  Matches  often  have  sulphur  on 
them,  and  the  smell  of  sulphur  burning  in  air  is  often 
called  the  smell  of  burning  matches.  Moisten  a  piece  of 
blue  litmus-paper  with  some  of  the  solution  in  the  cylin- 
der.    To  what  colour  does  the  paper  turn  ? 

In  another  cylinder  of  oxygen  perform  a  similar  experi- 
ment with  phosphorus.  Phosphorus  is  very  easily  set  on 
fire,  so  must  be  handled  very  carefully.  Cut  off  under 
water  a  small  piece  of  phosphorus,  say  half  the  size  of  a 
pea  or  less.  Why  is  phosphorus  kept  under  water,  and 
why  must  it  be  under  water  when  it  is  cut  ?  *  Are  potas- 
sium and  sodium  kept  under  water  to  protect  them  from 
the  air  ?  Dry  the  small  piece  of  phosphorus  on  blotting- 
paper  or  filter-paper  by  laying  it  on  the  paper,  which  is 
then  folded  over  it  without  rubbing  the  phosphorus. 
Why  should  the  phosphorus  be  dried  ?  Why  should  it 
be  dried  on  bibulous  paper,  such  as  blotting-paper  or  filter- 
paper?  Put  the  phosphorus  into  a  deflagrating  spoon 
and  heat  gently  until  it  begins  to  burn,  and  then  plunge 

*  Phosphorus  inflames  so  readily  and  burning  phosphorus  inflicts  such 
severe  wounds  that  beginners  are  often  warned  not  to  take  it  in  their  fin- 
gers except  when  it  is  under  water,  but  to  hold  it  in  nippers.  When  held  in 
nippers,  however,  the  phosphorus  is  liable  to  be  more  carelessly  handled, 
and,  therefore,  more  frequently  to  catch  fire  inopportunely.  In  whatever 
way  phosphorus  is  handled,  the  greatest  care  must  be  exercised. 


OXVGEN^ 


33 


ces  that 
o  burn, 
le  burn- 
oes  the 
sulphur 
[ler,  and 
r  or  of 
m,  what 
phur  on 
is  often 
piece  of 
le  cylin- 

r  experi- 
ly  set  on 
>ff  under 
size  of  a 
iter,  and 
re  potas- 
em  from 
blotting- 
which  is 
isphorus. 
should  it 
or  filter- 
g   spoon 
plunge 

flicts  such 

In  their  fin- 

|hen  held  in 

|y  handled, 

whatever 


into  a  cylinder  of  oxygen.  Wliat  does  the  smoke  look 
like  ?  As  soon  as  the  pliosphorus  has  ceased  burning, 
remove  it  from  the  cylinder,  pour  in  a  little  water,  and 
shake.  What  happens  to  tlie  fumes  ?  Taste  a  drop  of 
the  water.  What  taste  has  it  ?  How  does  it  act  on  blue 
litmus-paper  ?  Substances  that  have  a  sour  taste  and  tliat 
redden  blue  litmus  are  called  acids.  Test  with  litmus 
the  liquids  in  the  bottles  given  you,  to  find  out  which  are 
acid,  which  alkaline,  and  wliich  neutral,  that  is,  neither 
acid  nor  alkaline.  Add  lime-water  to  some  of  the  water 
in  the  cylinder  and  compare  witli  tlie  result  obtained 
after  burning  carbon.  Lavoisier,  tlie  celebrated  Frencli 
chemist,  who,  though  lie  did  not  discover  oxygen,  was  the 
most  thorough  investigator  of  its  character,  thought  that 
all  acids  contained  it,  and  so  gave  to  the  gas  the  name 
oxygen,  which  means  acid  producer.  It  was  later  found 
that  all  acids  do  not  contain  oxygen,  but  the  name  was 
retained.  The  name  hydrogen,  as  already  stated,  is  also 
due  to  Lavoisier. 

Set  fire  to  a  piece  of  sodium  in  a  deflagrating  spoon  and 
introduce  it  into  another  cylinder  of  oxygen.  What  is 
the  colour  of  the  flame,  and  what  appearance 
have  the  fumes?  Pour  a  little  water  into  the 
cylinder  and  test  the  solution  with  litmus.  Is  it 
acid,  or  alkaline,  or  neutral  ? 

Heat  a  watch-spring  in  a  flame  and  straighten 
it,  leaving  a  little  of  the  spiral  at  one  end,  or  use 
instead  a  piece  of  picture-cord  wire.  Dip  the 
end  into  sulphur,  light  it,  and  introduce  the  wire 
into  a  cylinder  of  oxygen  having  water  about  an 
inch  deep  in  the  bottom,  as  shown  in  Fig.  15.  Notice  how 
the  iron  burns.    Does  it  give  off  fumes  like  sulphur,  phos- 


Fia.  15 


84 


VIIEMISTUY 


phoriis,  and  sodium  ?  Does  it  have  a  flame  ?  What  hap- 
pens to  the  product  of  combustion  ?  VVJiy  were  you  tokl 
to  have  water  in  the  bottom  of  the  cylinder  ?  'J'ake  out 
the  pieces  of  solid,  wash  them  oft',  and  test  them  with  lit- 
mus-paper. Is  the  litmus  affected  ?  Can  you  give  any 
reason  why  you  might  have  expected  the  result  obtained  ? 
Is  the  solid  soluble  in  water  ?  What  was  the  reason  for 
washing  it  off  before  testing  it  with  litmus?  What  is  in 
solution  in  the  water  in  the  cylinder?  Does  this  com- 
pound of  iron  and  oxygen  look  like  red  hematite,  which 
you  have  already  proved  to  be  a  compound  of  iron  and 
oxygen  ?  What  difference,  if  any,  is  tliere  in  the  action 
of  each  of  these  oxides  toward  a  magnet?  What  proper- 
ties have  you  noticed  of  the  oxides  examined,  of  carbon, 
sulphur,  phosphorus,  sodium,  and  iron  ? 

Residue  after  Preparation  of  Oxygen.  —  If  you  have  not 
already  made  sure  that  all  of  the  oxygen  has  been  given 
off  from  the  mixture,  heat  it  once  more  till  no  move  gas  is 
evolved.  When  the  residue  is  cool,  add  enough  v;ater  to 
dissolve  out  all  except  the  black  substance,  and  filter.  Is 
what  remains  on  the  filter  like,  or  is  it  not  like,  one  of 
the  substances  put  into  the  mixture  ?  What  is  it  ? 
Evaporate  the  filtrate  to  dryness.  What  part  of  the 
original  mixture  does  it  most  resemble  ?  Is  it  exactly 
the  same  ?  Does  it  weigh  more  or  less  ?  Find  out 
approximately  how  the  weights  compare.  Compare  also 
the  taste  of  the  substance  with  that  of  i^otassium  chlorate. 
Take  equal  amounts  of  the  two  substances  in  separate 
test-tubes,  and  add  just  enough  w^ater  to  dissolve  each  of 
them  in  the  cold.     Which  is  the  more  soluble  ? 

Statement  regarding  the  Occurrence  and  Properties  of 
Oxygen.  —  Oxygen  is  not  only  found  in  water  and  in  air, 


Hiat  hap- 
yoii  told 
'i'like  out 
.  with  lit- 
gWe  any 
)btaiiied  ? 
'easoii  for 
riiat  is  ill 
his  coin- 
te,  which 
iron  and 
he  action 
t  projjcr- 
f  carbon, 

iiave  not 
en  given 
)re  gas  is 
water  to 
Iter.  Is 
3,  one  of 

•  ■■  I  o 

is      11  ; 

of  the 
exactly 
lind  out 
Lire  also 
Ihlorate. 
jeparate 
each  of 

Irties  of 
in  air, 


OXYGEN 


35 


but  it  forms  about  one-half  of  the  solid  crust  of  the  earth, 
so  that  it  is  the  most  abundant  substance  in  nature.  It 
forms  part  of  every  vegetable  and  animal  tissue.  It  is 
not  easy  to  se[)arate  it  from  the  great  majority  of  its  com- 
pounds, and  so  comparatively  expensive  substances  are  used 
for  its  manufacture. 

It  is  a  colourless,  odourless,  tasteless  gas  at  the  ordinary 
temjjerature.  It  was  first  liquefied  in  very  small  quantities 
in  18TT  ;  it  can  now^  be  obtained  licpiid  by  tlie  gallon.  It 
boils  at  —  181°  C  It  is  just  a  little  more  soluble  in 
water  than  hydrogen  is,  100  volumes  of  water  taking 
up  about  3  volumes  of  oxygen  at  the  ordinary  tempera- 
ture.* The  solubility  of  oxygen  in  water  is  very  impor- 
tant, for  it  is  the  dissolved  oxygen  that  enables  lish  to 
live.  If  water  is  boiled,  to  drive  out  the  oxygen,  and 
then  cooled  in  absence  of  air,  lish  cannot  live  in  it. 

Oxygen  is  the  part  of  the  air  tliat  supports  life,  but  if 
the  air  were  all  oxygen  the  actions  of  life  would  go  on  too 
rapidly.  In  some  cases,  however,  it  is  used  in  hospitals 
for  patients  in  whom  respiration  needs  to  be  stimulated. 
Oxygen  is  slightly  heavier  tliiin  air  and  sixteen  times  as 
heavy  as  hydrogen. 

Oxygen  is  necessary  not  only  for  life  but  for  the  combus- 
tion of  all  ordinary  fuels.  Its  most  striking  chemical 
property  is  the  number  of  substances  with  Avhich  it  can 
combine,  and  the  very  firm  compounds  which  it  makes 
with  many  of  them. 

*  Gases  are  more  soluble  at  lower  temperature  than  at  higher,  and 
hence,  when  the  solubility  is  given,  the  temperature  should  be  indicated. 
Hydrogen  between  the  temperatures  0°  C.  and  25°  C.  was  said  to  be  an 
exception,  the  solubility  being  the  same  at  all  temperatures  within  that 
limit,  but  later  investigations  show  that  it  follows  the  general  rule. 


i 


30 


(  IIEMlSTUr 


You  have  learned  that  when  it  combines  witli  an  element, 
the  compound  is  called  an  oxide,  and  sometimes  it  com- 
bines with  an  element  in  several  proportions,  —  that  is, 
there  are  several  oxi(U;s  of  the  one  element.  These  oxides 
liave  different  cliaracters,  sometimes  very  different  indeed. 
The  properties  of  a  substance  depend  not  only  on  tlie 
elements  whicli  compose  it,  but  also  upon  the  j)roporti()ns 
of  the  element.  'I'his  yon  saw  ilhistrated  in  the  case  of 
hematite  and  tlie  other  oxide  of  iron  which  has  tlie  same 
com})osition  as  the  mineral  majj^netite. 

Ozone.  —  When  electric  sparks  are  passed  through 
oxygen,  a  small  (piantity  of  the  gas  is  clianged  and  acquires 
a  very  strong  smell.  The  new  substance  is  called  ozone, 
from  a  Greek  word  wliicili  means  a  smell.  Tliough  ozone 
is  made  from  oxygen,  this  fact  does  not  prove  that  oxygen 
is  not  a  simple  su})stance,  for  tliere  is  no  loss  in  weight, 
and  on  being  heated  to  a  tem})erature  of  300°  C.  the  ozone 
is  reconverted  into  oxygen.  The  same  simple  substance 
can  appear  in  two  forms,  one  of  which  is  called  oxygen, 
the  other  ozone.  They  are  said  to  be  allotropic  forms 
(from  the  Greek  word  meaning  "  another  f(U'm "),  or, 
since  oxygen  is  the  more  common,  ozone  is  often  said  to 
be  an  allotropic  form  of  oxygen. 

The  properties  of  ozone  and  oxygen  are  very  different 
in  many  respects.  Ozone  is  one  and  one-half  times  as 
heavy  as  oxygen.  It  acts  more  readily  on  most  substances 
than  oxygen  does;  for  instance,  silver,  which  is  not  acted 
on  by  oxygen,  is  acted  on  by  ozone,  forming  silver  oxide. 
It  also  acts  on  potassium  iodide,  setting  free  iodine,  wliich 
gives  a  blue  colour  to  starch.  A  usual  test  for  ozone  is 
a  piece  of  filter-paper  moistened  with  a  solution  of  potas- 
sium iodide  and  starch.     If  ozone  is  present  the  paper 


i 


ti 
ei 
til 


OAYGKN 


37 


?leinent, 

it  com- 
tliat  is, 
e  oxides 

indeed. 

on  the 
portions 

case  of 
lie  same 

through 

icquires 

d  ozone, 

;li  ozone 

oxygen 

weight, 

e  ozone 

bstanee 

)xygen, 

forms 

),    or, 

said  to 

[fferent 

imes  as 

stances 

acted 

1  oxide. 

wliicli 

tone  is 

Ipotas- 

paper 


turns  blue.  Such  papers  are  often  used  to  test  tiie  pres- 
ence of  ozone  in  the  atmosphere.  Some  otlier  gases  also  givi 
the  blue  colour  to  starcli  paper,  and  unless  they  are  known 
to  be  absent  the  test  is  not  sutlicient.  Many  coloured  sub- 
stances become  colourless  if  oxygen  is  added  to  them. 
Ozone  is  a  form  of  the  element  which  acts  on  these  coloiu's 
more  readily  than  ordinary  oxygen  does,  and  takes  away 
the  colour,  or,  as  we  usually  say,  hh'nchvs.  Hence  ozone  is 
sometimes  used  as  a  bleachint/  ai/enf,  though  some  other 
bleaching  agents  are  more  imjjortant.  Ozone  is  also 
sometimes  enndoyed  in  tlie  rejininfi  of  oils  and  for  other 
industrial  purposes.  It  will  probably  come  into  extensive 
use,  now  that  electrical  power  is  so  widely  emj)loyed. 
Ozone  can  be  made  in  other  ways,  but  none  of  them  are  so 
cheap  or  so  satisfactory.  Ozone  destroys  the  disagreeable 
odour  of  many  substances,  and  is  therefore  used  as  a 
disinfectant. 

Not  only  is  ozone  produced  by  ordinary  electric  machines, 
but  it  is  made  on  the  large  scale  by  electric  discharges  in 
the  atmosphere.  This  is  one  reason  why,  after  a  tliunder- 
storm,  the  air  seems  so  pure  and  fresh.  There  is  less 
ozone  in  cities  than  in  the  country,  because  it  is  more 
quickly  used  up  in  cities.  The  air  over  the  ocean  contains 
a  comparatively  large  amount  of  ozone,  and  there  is  very 
good  reason  to  think  that  the  action  of  ozone  has  a  great 
deal  to  do  with  the  phosphorescence  so  frequently  seen 
at  sea. 

Ozone  can  be  condensed  to  a  liquid,  in  which  condi- 
tion it  is  of  an  indigo  blue  colour.  The  liquid  boils  at 
—  119°C.,  and  the  vapour  has  a  slightly  blue  tinge.  It 
has  been  suggested  that  the  colour  of  the  sky  is  caused  by 
ozone. 


38 


CHEMISTRY 


I 


Hydrogen  Peroxide.  —  Water  is  an  oxile  of  liydrogen, 
but  there  is  another  oxide  which  contains  more  oxygen 
in  proportion  to  the  hydrogen  and  is  called  hydrogen 
peroxide.  The  prefix  "per"  is  a  contraction  for  "hyper," 
as  in  the  word  hypercritical.  The  term  "  peroxide  "  denotes 
that  there  is  a  large  amount  of  oxygen  in  the  substance. 
In  hydrogen  peroxide  there  is  twice  as  much  oxygen  in 
proportion  as  in  water,  and  it  is  sometimes  called  hydrogen 
dioxide  to  show  this  fact.  Tn  hydrogen  peroxide  the 
hydrogen  and  oxygen  are  not  so  firmly  united  as  in  water. 
We  might  expect  that  this  would  be  the  case,  because  if 
it  w(!re  not,  hydrogen  peroxide  would  probably  be  as 
common  as  water.  Since  hydroge  \  peroxide  is  nnt  so 
firm  a  compound  as  water,  in  other  words  is  not  so  stable, 
it  might  be  expected  to  give  up  part  of  its  oxygen  to  other 
substances.  Tliis  it  does,  acting  as  an  oxidising  agent 
and  being  itself  reduced  to  v/ater.  Hydrogen  peroxide  is 
therefore  used  in  bleaching,  being  sometimes  more  con- 
venient for  that  purpose  than  ozone.  It  is  also  a  disin- 
fectant and  is  used  in  surgery. 

Like  water,  hydrogen  peroxide  is  a  liquid,  but  it  is 
heavier  than  water.  T^  readily  decomposes  into  water 
and  oxygen,  and  is  used  in  dilute  solution  because  more 
stable  in  that  condition.  The  ordinary  commercial  solu- 
tion in  water  contains  about  8%  of  the  peroxide,  but 
lately  with  very  special  manipulation  and  precaution 
a  liquid  has  been  obtained  that  contains  99%  of  hydrogen 
peroxide. 


I 


plrogen, 
oxygen 
ydrogen 
'  liyper," 
'  denotes 
bstance. 
ygen  in 
ydrogen 
ddc  the 
n  water, 
jcause  if 
y  be  as 
s  nnt  so 
o  stable, 
to  other 
g  agent 
oxide  is 
lore  con- 
a  disin- 

ut  it  is 
water 
ic  more 
al  solu- 
de,  but 
caution 
drogen 


CHAPTER   IV 


NITROGEN 


We  liave  found  that  the  air  contains  oxygen,  but  that 
it  is  not  pure  oxygen,  because  substances  do  not  burn  in 
it  so  readily  as  in  tlie  pure  oxygen  that  we  prepared. 
Which  substance 
burned  most  read- 
ily in  oxygen? 
Which  substance 
required  the  most 
care  in  handling  ? 
Phosphorus  is  the 
best  substance  for 
rapidly  taking 
away  oxygen  from 
the  air. 

Action  of  Phos- 
phorus on  Air.  — 
Experiment  20.  — 
Just  as  carefully 
as  before,  cut  oft' 
a  piece  or  two  of  — 
phospliorus  (about 
half  the  size  of  an  apple  seed),  dry  and  put  into  a 
small  porcelain  dish  floating  in  a  pneumatic  trough.  Set 
fire  to  the  jdiospliorus  and  immediately  place  over  it 
an  inverted  cylinder  as  in  Fig.  10.  Do  bubbles  escape 
from  the  cylinder?     If  so,  why?     If  not.  what  prevents 

80 


Fio.  IG 


40 


CHEMISTRY 


them  escaping  in  your  experiment  ?  Does  the  flame  of 
the  phosphorus  grow  more  or  less  bright?  Does  it  grow 
hirger  or  smaller  ?  Why  ?  What  is  the  appearance  of  the 
fumes  in  the  cylinder  ?  Allow  to  stand  for  a  few  minutes. 
What  becomes  of  the  fumes  ?  Put  a  piece  of  litmus-paper 
into  the  cylinder  and  see  what  colour  it  assumes.  Notice 
the  height  of  the  water  in  the  cylinder.  Why  has  tlie 
water  risen  ?  Remove  the  cylinder  from  the  pneumatic 
trough  and  test  the  gas  with  a  lighted  match  or  taper. 
Does  the  match  continue  to  burn  ?  Does  the  gas  take  fire  ? 
Is  the  gas  a  supporter  of  combustion  ?  Is  it  combustible  ? 
Experiment  21.  Invert  a  graduated  cylinder  over 
the  ])neumatic  trough.      Allow  air  to  escape  till  there 

is  100  c.c.  or  200 
c.c.  (as  may  be 
most  convenient) 
in  the  cylinder, 
the  water  being 
at  the  same  level 
inside  and  out- 
side. Taive  the 
reading  carefully. 
Then  introduce  a 
piece  of  phospho- 
rus as  large  as  a 
bean  or  larger, 
supported  on  a 
wire  so  that  it 
will  IJe  above  the 
surface  of  the 
water  (Fig.  17  shows  the  apparatus,  a  stick  of  phosphorus 
being  represented).     After  a  day  or  two  remove  the  phos- 


FiQ.  17 


i 


^ 


flame  of 

it  grow 

3e  of  the 

minutes. 

as -paper 

Notice 

has  the 

eumatic 

r  taper. 

ike  fire  ? 

ustible  ? 

er  over 

11  there 

.  or  200 

may   be 

enient) 

y^linder, 

being 

le  level 

out- 

ive   the 

refully. 

)cluce  a 

lospho- 

l^e  as  a 

larger, 

on    a 

hat    it 

ve  the 

the 

horus 

phos- 


I 


NITROGEN 


41 


phoriis  and  again  measure  carefully  the  volume  of  the  gas, 
the  level  of  the  water  inside  and  outside  being,  as  before, 
the  same.  Assuming  that  the  oxygen  has  all  been  removed 
by  the  phosphorus,  what  does  your  experiment  show  you 
as  to  its  proportion  by  volume  in  the  air  ? 

Copper  heated  in  Current  of  Air.  —  Exi»eiument  22.  Fit 
up  an  apparatus  as  in  the  figure  (Fig.  18).  In  the  bulb 
of  the  glass  tube,  as  shown  at  the  left  of  the  figure,  place 


Fkj.  18 


fine  copper  filings.  Put  the  tube  into  position  and  ipply 
heat.  When  the  copper  is  red  hot,  pass  air  shnvly  o\qv  it, 
allowing  time  for  the  copper  to  act  on  the  air.*  One  of 
the  easiest  ways  to  provide  the  current  of  air  is  by  means 
of  an  as})irator.  A  form  of  aspirator  that  may  be  used  is 
shown  in  the  figure.      A  bottU;  lilled  with  water  is  fitted 

*  Unless  the  copper  is  porous  it  may  become  so  coatcrl  with  oxide  as  to 
be  ineffectuiil.  This  is  avoitled  by  passinj^  the  air  tliroufi;lj  ammonia  water. 
If  tliis  is  (Ume.  liowever.  (he  appearance  of  tlie  copper  will  not  be  much 
changed,  the  oxide  not  \m\\%  produced,  and  the  further  experiment  of 
passing  hydrogen  over  the  oxide  cannot  be  performed. 


A 


42 


CHEMISTRY 


with  a  cork  having  two  holes,  through  one  of  which  a  tube 
passes  to  the  bottom  of  the  bottle.  This  tube  has  attached 
to  it  a  rubber  tube  long  enough  to  act  as  a  siphon  and 
closed  by  a  pinch-cock  or  screw-clamp.  A  short  tube 
passes  just  through  the  other  hole  in  the  cork  and  is  con- 
nected with  the  larger  tube  containing  the  copper.  As 
the  water  is  allowed  to  flow  out  of  the  bottle  air  is  drawn 
in,  and  its  flow  r  ay  be  regulated  by  the  pinch-cock.  Tl.»e 
figure  represents  the  water  as  flowing  into  a  second  bottle. 
The  pinch-cock  on  the  tube  between  the  bottles  is  omit- 
ted in  t'lis  diagram  but  is  shown  in  the  next.  The 
current  of  air  is  from  lefl  to  right.  When  you  have 
collected  a  sufficient  quantity  of  the  gas,  transfer  some  of 
it  to  a  cylinder  or  test-tube.  Figure  19  shows  one 
method  of  doing  this ;  the  bottle  containing  the  gas  being 
now  placed  on  the  table  and  the  other  ont  on  the  block. 

Experiments  with  Nitrogen.  —  Find  out  whether  the 
gas  has  any  smell,  taste,  or  colour,  and  try  its  effect  on  a 
burning  match.  Add  to  another  test-tube  or  cylinder  full 
of  the  gas,  a  little  lime-water  or  baryta-water.  Is  there 
or  is  there  not  any  change  in  the  solution  ?  This  experi- 
ment is  for  the  purpose  of  comparison  at  a  later  date. 
The  gas  that  you  have  prepared  is  nitrogen.  What  is 
the  appearance  of  the  substance  in  the  glass  bulb?  Is 
it  copper  ?  Without  removing  it,  pass  hydrogen  over  it 
and  heat.  What  passes  out  from  the  bulbed  tube  ?  What 
does  the  hydrogen  remove  from  the  black  substance  in  tbe 
tube  ?    What  name  would  you  give  to  this  black  substance  ? 

Nitrogen,  is  slightly  lighter  than  air.  It  is  less  soluble 
in  water  than  oxygen  is ;  100  volumes  of  water  dissolve  1 J 
volumes  of  nitrogen  at  the  ordinary  temperature.  Nitro- 
gen can  be  condensed  to  a  liquid,  which  boils  at  —193°  C. 


tl 
ft 
tl 
t( 
a 
ii 
0 


ich  a  tube 
(  attached 
phon  and 
lort  tube 
id  is  con- 
'per.     As 
is  drawn 
CK.     ±  !)e 
id  bottle, 
is  omit- 
:t.      The 
^ou  have 
.'  some  of 
ows   one 
^as  being 
block, 
ther    the 
ect  on  a 
ider  full 
Is  there 
experi- 
er  date. 
iVhat  is 
lib  ?     Is 
over  it 
What 
in  the 
tance  ? 
Isoluble 
)lve  11 
Nitro- 
93°  C. 


NITROGEN 


43 


( 


i 


Argon.  —  We  have  found  that  nitrogen  exists  in  the 
air.  It  is  found  in  many  other  substances,  among  them 
many  tissues  of  plants  and  animals,  though  not  existing 
in  all  the  tissues  as  oxygen  and  hydrogen  do. 

From  these  substances  the  nitrogen  can  be  obtained, 
and  a  few  years  ago  it  was  discovered  by  Lord  Rayleigh 
that  nitrogen  so  obtained  is  very  slightly  less  dense  than 
nitrogen  obtained  from  air.     This  led  him  to  conjecture 


Fia.  19 

that  the  nitrogen  obtained  from  air  is  not  pure,  and  Pro- 
fessor Ramsay  and  Rayleigh  succeeded  in  separating  from 
the  nitrogen  of  tlie  air  a  substance  which  is  not  known 
to  combine  with  anything  else  and  to  which  the  name 
argo7i^  iiKn^ning  inert,  was  given.  Further  experiment 
indicated  that  what  was  first  called  argon  contains  small 
quantiiies  of  other  inert  gases.  Why  is  there  no  argon 
in  the  nitrogen  which  is  obtained  from  compounds  ? 


44 


CHEMISTRY 


\m 


Composition  of  Air.  —  Air  consists  mainly  of  oxygen  and 
nitrogen.  The  proportions  of  oxygen  and  nitrogen  in  air 
are  not  exactly  the  same  at  all  times  in  any  one  place, 
nor  are  they  exactly  the  same  in  all  places  at  any  one 
time,  but  the  variations  are  within  very  narrow  limits. 
When  Scheele  discovered  nitrogen  in  1772  he  called  it 
"  vitiated  air,"  because  he  found  that  when  the  ••'  fire  air  " 
was  removed  from  ordinary  atmospheric  air,  what  was  left 
behind  could  not  support  life.  Hence,  wiien  later  on 
experiments  were  made  to  find  out  the  proportions  of 
oxygen  and  nitrogen  in  air,  the  apparatus  used  was  called 
a  eud{o7neter^  which  means  measurer  of  goodness. 

The  variations  in  the  amounts  of  oxygen  and  nitrogen 
in  the  air  are  not  large  enough  to  make  any  difference  in 
it:^  wholesomeness,  but  the  name  has  been  retained  for 
this  apparatus,  which  is  very  much  used  in  the  analysis 
of  gases.  One  form  consists  of  a  straight  graduated  tube 
closed  at  one  end,  and  provided  with  two  platinum  wires 
going  through  the  glass  so  that  an  electric  spark  can  be 
passed  between  them  through  the  gas  in  the  tube. 

In  order  to  find  out  the  proportions  of  oxygen  and 
nitrogen  (along  with  argon,  etc.)  in  the  air,  the  eudiom- 
eter is  filled  with  mercury,  inverted  over  a  mercury 
trough,  and  partially  filled  with  air  which  has  been  freed 
from  all  other  gases.  Sufiicient  hydrogen  is  then  passed 
in,  the  mixture  is  fired  by  an  electric  spark,  which  causes 
the  oxygen  and  hydrogen  to  unite  forming  water  whose 
volume  is  very  small,  and  the  volume  of  both  oxygen  and 
nitrogen  can  thus  be  determined.  Another  form  of  ap- 
paratus is  shown  in  Fig.  20.  There  are  a  great  many 
details  and  precautions  not  mentioned  in  this  description. 

In  the  case  of  oxygen  and  hydrogen,  you  saw  the  dif- 


(I 


f( 

C( 

a 


NITROGEN 


45 


gen  and 
3n  in  air 
le  place, 
any  one 
r  limits, 
jailed  it 
fire  air  " 
was  left 
later  on 
tions  of 
IS  called 

litrogen 
rence  in 
ned  for 
analysis 
ed  tube 
wires 
can  be 

|en  and 
iidioni- 
ercury 
1  freed 
passed 
causes 
whose 
n  and 
|of  ap- 
many 
ption. 
e  dif- 


ference between  a  mixture  and  a  compound.  Would  you 
consider  that  air  is  a  mixture  of  oxygen  and  nitrogen  or 
a  compound  ? 

Liquid  Air. —  Air  was  liquefied 
for  the  first  time  in  1877,  when 
a  few  small  drops  were  obtained. 
Now  it  is  manufactured  by  the 
gallon.  Liquid  air  has  many 
very  peculiar  and  interesting 
properties,  but  among  the  most 
interesting  are  the  effects  pro- 
duced by  its  extremely  low  tem- 
perature. If  liquid  air  is  put 
into  a  tin  cup  and  alloAved  to 
stand  till  the  cup  gets  quite 
cold,  the  latter  becomes  very 
brittle,  and  may  be  broken  in 
the  hand  more  easily  than  an 
ordinary  glass  dish  of  the  same 
thickness  would  be  at  the  ordi- 
nary temperature.  Mercury  freezes  in  liquid  air,  and  a 
nail  may  be  driven  by  a  hammer  made  of  the  frozen  metal. 
Bread  becomes  crisp,  like  very  dry  toast,  and  crumbles 
between  the  fingers.  Alcohol  freezes  to  an  ice  which 
looks  something  like  the  white  frosting  of  a  cjike. 

Perhaps  one  of  the  most  striking  experiments  is  boiling 
liquid  air  in  a  tea-kettle  over  a  gas-burner.  The  air  in 
boiling  keeps  the  kettle  so  cold  that  hoar  frost  collects 
on  it.  The  moisture  that  condenses  on  the  kettle  comes 
chiefly  from  the  gas  flame.  What  does  this  show  one  of 
the  constituents  of  gas  to  be  ?  If  the  kettle  uf  liquid  air 
is  taken  from  the  fire  and  a  cupful  of  water  poured  inio 


Fk;.  20 


46 


CHEMISTRY 


it,  the  air  boils  more  rapidly  than  when  heated  by  the  gas- 
burner,  because  the  water  mixes  with  the  air  and  heats  it 
throughout.  The  kettle  may  be  now  put  on  the  fire  again, 
and  ice  produced  by  the  freezing  of  the  water  taken  out 
of  it. 

Both  oxygen  and  nitrogen  boil  at  very  low  tempera- 
tures, but  nitrogen  boils  at  a  lower  temperature  than 
oxygen,  and  so  in  the  liquid  air  nitrogen  can  be  boiled 
off  from  the  oxygen,  just  as  alcohol  can  be  boiled  off  from 
water.  It  may  be  that,  sometime,  tlie  cheapest  way  of 
getting  oxygen  will  be  to  liquefy  air  and  boil  off  the 
nitrogen. 

Liquid  oxygen  is  somewhat  magnetic,  and  if  a  strong 
electromagnet  be  brought  down  over  liquid  oxygen,  the 
latter  rises  up  toward  the  magnet.  This  is  a  very  inter- 
esting property. 

Ammonia 

Destructive  Distillation.  —  Experiment  23.  Heat  a 
small  quantity  of  horn  or  lean  meat  or  hair  in  a  test- 
tube.  Notice  what  collects  in  the  upper  part  of  the  tube. 
What  evidence  is  there  that  the  substance  used  contains 
oxygen  and  hydrogen?  If,  when  you  distil  water  from 
a  salt  solution  in  a  flask,  you  pour  back  the  distillate  into 
the  flask,  would  the  liquid  produced  be  the  same  as  at 
first,  or  would  it  be  different  ?  If  the  substances  that  distil 
from  the  horn  or  meat  or  hair  were  brought  back  into  the 
test-tube,  would  the  original  substance  be  reproduced? 
When  by  heating  a  substance  the  products  of  distillation 
cannot  recombine  to  produce  the  original  substance,  there 
is  said  to  be  destructive  distillation.  When  meat  is  heated, 
is  there  simple  distillation  or  destructive  distillation  f 


) 


the  gas- 
heats  it 
e  again, 
ken  out 

empera- 
I'e  than 
3  boiled 
3ff  from 
way  of 
off'  the 

,  strong 
jen,  the 
y  inter- 


Heat  a 
a  test- 
e  tube, 
ontains 

from 
te  into 

as  at 
:  distil 
ito  the 
need  ? 
llation 

there 
leated, 


NITROGEN 


47 


Into  the  vapours  coming  off  from  the  test-tube  put  a 
strip  of  moistened  neutral  litmus-paper.  To  what  colour 
does  the  litmus  change  ?  What  does  this  show  ?  The 
substance  producing  this  effect  is  called  ammonia,  but  in 
this  case  it  is  mixed  with  a  number  of  other  substances. 

Laboratory  Preparation  of  Ammonia  and  Experiments  with 
the  Gas.  —  ExrERiMENT  24.  Test  a  crystal  of  sal-ammo- 
niac (ammonium  chloride)  with  moistened  litmus-paper 
to  find  out  whether  it  is  alkaline,  neutral,  or  acid.  Do 
the  same  with  a 
little  lime.  Mix  a 
few  grammes  of 
ammonium  chlo- 
ride with  about 
twice  its  weight  of 
lime,  and  introduce 
into  a  small  retort 
or  large  test-tube. 
Fit  up  the  appa- 
ratus so  that  you 
can  collect  any  gas 
coming  off  from  it, 
and  heat.  Hold  a 
piece  of  moistened 
litmus-paper  at  the 
mouth  of  the  de- 
livery-tube.  What 

evidence  have  you  j:liat  a  gas  is  being  produced  in  your 
apparatus  ?  Collect  the  gas,  not  over  water,  but  as  shown 
^in  Fig.  21,  in  a  test-tube  (or  small  cylinder)  by  inverting 
the  test-tube  and  putting  the  delivery-tube  of  your  appa- 
ratus far  up  into  the  test-tube,  whose  mouth  is  loosely 


Fio.  21 


48 


CHEMISTRY 


n 


closed  with  cardboard  or  a  loosely  fitting  cork.  When 
the  gas  is  coming  out  from  the  mouth  of  the  test-tul)e, 
you  should  remove  the  delivery-tube.  Now  close  the 
test-tube  with  «  tightly  fitting  cork,  and  collect  another 
test-tube  or  two  in  the  same  way. 

Put  into  the  ammonia  fumes  a  glass  rod  on  which  is 
a  drop  of  strong  hydrochloric  acid.  What  effect  is  pro- 
duced ?  Try  to  light  the  gas  as  it  escapes  from  the  mouth 
of  the  delivery-tube.     Does  it  bux'n?     What  effect  does 


I 


Fig.  22 

it  have  on  the  flame  of  the  taper  applied  to  it  ?  Ammonia 
burns  in  pure  oxygen,  and  if  you  have  some  oxygen  at 
hand  you  should  try  the  experiment,  and  compare  the 
appearance  of  the  flame  with  that  of  hydrogen.  Connect 
the  delivery-tube  with  a  glass  tube  containing  black  oxide 
of  copper,  as  shown  at  the  left  of  Fig.  22.  The  other  end 
of  the  tube  is  joined  with  a  U-tube  and  delivery-tube. 
Heat  the  copper  oxide.  What  do  you  notice  in  the 
U-tube  ?  When  enough  gas  has  been  collected  in  the  cyl- 
inder, test  it  by  smell  and  by  a  lighted  taper.  Is  it  ammo- 
nia ?     What  gas  is  it  like  ?     What  change  has  taken  place 


'1 


I 


« 


NITROGEN 


49 


When 
st-tube, 
Dse  the 
unother 

^hich  is 

is  pro- 

j  mouth 

ct  does 


Timonia 
/■gen  at 
[ire  the 
onnect 
k  oxide 
ler  end 
y-tube. 
in  the 
he  cyl- 
ammo- 
n  pLace 


in  the  copper  oxide  ?  What  did  the  copper  oxide  give  to 
tlie  aninionia  ?  What  must  have  been  in  the  ammonia  to 
produce  the  substcance  in  the  U-tube  ?  Of  wliat  two  ele- 
ments is  ammonia  composed  ?  Is  it  a  compound  of  these 
two  elements,  or  is  it  a  mixture  ? 

Now  hold,  mouth  downward,  one  of  the  test-tubes  of 
ammonia  that  you  collected.  Open  it  and  put  a  lighted 
tai)er  into  the  gas.  Is  it  combustible  ?  Is  it  a  supporter 
of  combustion  ? 

Put  another  test-tube,  mouth  downward,  into  the 
pneumatic  trough  containing  water.  Holding  the  tube 
iirmly,  remove  tlie  cork.  What  happens  ?  Why  did  you 
not  attempt  to  collect  ammonia  over  water  in  the  same 
manner  as  oxygen  and  hydrogen  are  collected  ? 

Statement  of  Occurrence,  Preparation,  and  Properties  of 
Ammonia.  —  Why  is  ammonia  sometimes  called  volatile 
alkali  ?  It  was  at  one  time  largely  made  from  horns  of 
the  hart  and  is  known  under  the  name  "  spirits  of  harts- 
horn." The  most  of  it  is  now  made  when  coal  is  distilled 
in  making  coal  gas.  It  is  formed  in  the  decay  of  most 
animal  tissues,  and  is  found  in  sewage.  Hence,  when 
water  is  found  to  contain  more  than  the  very  smallest 
traces  of  ammonia,  it  is  considered  unfit  for  drinking 
purposes,  because  tlie  ammonia  probably  comes  from 
sewage  or  from  decaying  matter. 

Ammonia  is  a  very  important  fertiliser,  because  it  pro- 
vides nitrogen  for  plants  which  are,  for  the  most  part, 
unable  to  take  it  from  the  air.  Th«  fertiliser  used  is  not 
pure  ammonia,  but  its  compound  with  sulphuric  acid,  very 
similar  in  appearance  to  the  ammonium  chloride  with 
which  you  have  experimented. 

It  must  not  be  considered  that  ammonia  exists  as  such 
v 


60 


(  riKMlSTh'Y 


ill  coal  or  in  horn  and  is  merely  driven  out  by  heat.  It 
is  made  from  the  nitrogen  and  hydrogen  compounds  that 
exist  in  these  substances.  When  they  are  lieated,  the 
nitrogen  and  hydrogen  compounds  decom))ose  and  the 
two  elements  combine  in  the  process  of  distilhition,  tliougli 
free  nitrogen  and  hydrogen  gases  do  not  readily  cond)ine 
to  form  ammonia.  In  ammonium  chloride  ammonia  may 
be  said  to  exist  ready  formed.  When  ammonium  chloride 
is  heated  it  breaks  up  directly  into  ammonia  and  hydro- 
chloric acid,  two  gases  which  can  be  separated  from  each 
other  at  least  partially,  but  if  allowed  to  cool  witliout 
being  separated  reunite  to  form  annnonium  chloride  again. 
When  substances  decompose  in  this  way  by  heat  alone, 
recombining  on  cooling  to  form  the  original  substance, 
they  are  said  to  dissociate. 

Some  of  the  properties  of  ammonia  yjn  already  know. 
What  reason  have  you  to  believe  that  it  is  lighter  than 
air  ?  It  is  only  a  little  more  than  half  as  heavy  as  air. 
Though  —  like  hydrogen,  oxygen,  and  nitrogen  —  it  is 
colourless,  it  is  neither  tasteless  nor  odourless.  It  is,  as 
3^ou  found,  very  soluble  in  water,  which  dissolves,  at  the 
ordinary  temperature,  not  far  from  one  thousand  times 
its  volume  of  the  gas.  The  solution  of  ammonia  in  water 
is  called  ammonia  water  or  ammonia  liquor. 

When  ammonia  water  is  boiled  long  enough,  all  of  the 
ammonia  can  be  driven  off,  the  water  left  behind  contain- 
ing no  ammonia.  During  the  process,  some  of  the  water 
is  volatilised  with  the  ammonia.  Gases  which  are  easily 
dissolved  are  usually  easily  condensed.  Ammonia  can 
be  condensed  by  a  pressure  of  seven  atmospheres  at  the 
ordinary  temperature  or  without  additional  pressure  by 
cooling  to  —  38°  C.     Liquid   ammonia  (which   must   be 


1/ 


d 

ei 

al 

in 

ii 

n( 

pi 

so 

j'i 


yirmxjKX 


51 


eat.  It 
tids  that 
ted,  the 
and  the 
,  though 
combine 
»nia  nuiy 
chloride 

I  hydro- 
om  eacli 

without 
le  again, 
it  alone, 
ibstance, 

y  know. 

ter  than 
as  air. 
—  it  is 
It  is,  as 
1,  at  the 

Id  times 
n  water 

II  of  the 

jontain- 

le  water 

easily 

Ilia   can 

at  the 

mre  by 

lust   be 


I 
If 


I 


* 


•i 


I 


distinguished  from  annuonia  lic^uor)  is  used  for  refrig- 
erating purposes,  such  as  maliing  artificial  ice,  because  it 
absorbs  heat  in  evaporating.  In  some  apartment  houses 
in  New  York  and  elsewliere,  the  ammonia  is  used  to  cool 
a  liquid  (sucli  as  calcium  chloride  solution)  which  does 
not  freeze  so  easily  as  water.  This  licpiid  passes  through 
pipes  to  the  dilfereut  refrigerators  all  over  tlie  building  ; 
so  that  we  may  say  that  cold  is  sup[)lied  to  the  tenants 
just  in  the  same  way  as  heat  is.  It  seems  rather  curious 
at  lirst  siglit  that  in  order  to  provide  the  low  temperature 
a  steam  engine  should  ))e  used,  but  it  is  evident  that  the 
liquid  amuKHiia  that  evai)orates  must  be  recondensed,  and 
so  requires  work  to  be  done  u[)on  it. 

Liquid  ammonia  does  not  produce  so  low  a  temperature 
as  liquid  air,  and  hence  is  not  so  powerful  a  cooling  agent, 
but  it  is  more  easily  manufactured  and  more  easily  pre- 
served than  liquid  air.  On  the  other  hand,  on  account 
of  its  smell,  it  must  be  kept  in  closed  vessels,  whereas,  of 
course,  liquid  air  may  be  left  open. 

The  chemical  properties  of  ammonia  depend  partly  on 
its  being  a  compound  of  nitrogen  and  hydrogen.  It  burns 
in  oxygen  because  hydrogen  has  so  great  an  aihnity  for 
oxygen  that  the  heat  produced  can  keep  the  ammonia  at 
the  kindling  or  iynition  temperature.  When  substances 
combine  readily,  they  produce  heat  in  combining,  but  if 
the  substances  are  kept  cold  enough  they  will  not  combine. 
Phosphorus,  though  it  burns  so  readily,  will  not  combine 
with  oxygen  if  it  is  kept  cold;  but  if  one  part  of  it  be- 
comes hot  enough  to  combine  with  oxygen,  so  much  heat 
is  produced  that  the  next  part  of  the  phosphorus  is  made 
hot  enough  to  combine  with  the  oxygen,  that  is,  reaches 
its  Mndling  temperature.     In  the  case  of  ammonia,  when 


62 


CEEMISTRY 


it  is  lighted  in  an  atmosphere  of  pure  oxygen  at  the 
ordinary  temperature,  the  heat  produced  by  the  burning 
of  the  hydrogen  is  enough  to  heat  the  next  part  of  the 
ammonia  to  the  kindling  temperature,  and  so  a  jet  of 
ammonia  once  lighted  continues  to  burn  in  oxygen.  Air 
contains  so  much  nitrogen  that  the  heat  jjroduced  by  the 
union  of  the  hydrogen  in  the  ammonia  and  the  oxygen 
of  the  air  is  not  enough  to  raise  the  temperature  of  the 
ammonia  and  tlie  neighbouring  air  high  enough  to  cause 
them  to  combine,  and  so  a  jet  of  ammonia  does  not  con- 
tinue to  burn  in  air  unless  a  flame  is  constantly  applied. 
A  mixture  of  nitrogen  and  hydrogen  in  exactly  the  same 
proportion  as  they  exist  in  ammonia  would  continue  burn- 
ing in  air  if  once  lighted,  thus  showing  that  heat  must  be 
required  for  the  decomposition  of  ammonia  into  its  ele- 
ments, and  since  some  heat  is  required  for  decomposition 
of  the  ammonia,  the  tem2)erature  caused  by  the  burning 
of  the  hydrogen  is  not  so  high  as  when  all  the  heat  is 
applied  to  raising  the  temperature  of  the  gases.  When 
ammonia  burns,  the  main  part  of  the  combustion  is  due 
to  the  hydrogen  uniting  with  oxygen  ;  almost  all  of  the 
nitrogen  being  set  free,  thougli  a  very  small  portion  may 
combine  with  oxygen. 

The  weight  of  nitrogen  in  ammonia  is  to  the  weight  of 
hydrogen  in  the  ratio  of  14  to  3.  The  experiment  to 
prove  this  is  not  very  easy  to  carry  out,  but  it  is  merely 
a  modification  of  the  one  you  did  in  passing  ammonia  over 
hot  copper  oxide. 

Annnonia  gas  may  be  decomposed  by  electric  sparks  in 
a  eudiometer,  and  the  volume  of  the  nitrogen  and  hydro- 
gen produced  is  twice  that  of  the  ammonia.  By  putting 
in  enough  pure  oxygen  with  the  gases  and  passing  an 


I 


eaf- 


yiTIiOGEN 


53 


L  at  the 
burning 
t  of  the 
a  jet  of 
en.  Air 
d  by  the 

oxygen 
e  of  the 
to  cause 
not  con- 
applied. 
;he  same 
ue  burn- 
must  be 

its  ele- 
iposition 
burning 

heat  is 

When 

is  due 

of  the 

ion  may 


electric  spark,  the  hydrogen  is  all  used  up  and  it  is  found 
that  the  volume  of  the  nitrogen  left  is  just  one-quarter 
that  of  the  nitrogen  and  hydrogen  together,  and  therefore 
the  hydrogen  must  be  three-quarters;  in  other  words,  the 
volume  of  the  hydrogen  obtained  from  ammonia  is  three 
times  that  of  the  nitrogen. 

There  are  other  chemical  properties  of  ammonia  that 
could  not  be  predicted  from  its  composition  any  more 
easily  than  its  odour  could.  Ammonia  combines  readily 
with  acids  producing  substances  in  many  respects  like 
common  salt,  and  hence  called  salts.  This  was  what  you 
saw  happen  when  you  put  the  rod  moistened  witli  hydro- 
chloric acid  into  the  fumes  of  ammonia.  The  two  sul)- 
stances,  the  gaseous  hydrochloric  acid  given  off  from  the 
drop  of  solution,  and  the  gaseous  annuonia,  united  to  form 
a  white  smoke  of  solid  ammonium  chloride. 


eight  of 
inent  to 
merely 
nia  over 

3arks  in 
hydro- 
putting 
iing  an 


I 


'i- 


o 

fl 


CHArXER  V 

CARBON  DIOXIDE  AND  MONOXIDE 

Effect  of  the  Breath  on  Lime-water.  —  ExPERiisrENT  25. 
Pass  the  breath  I'loiii  the  lungs,  for  two  or  three  niiii'ites, 
through  about  10  c.c.  of  baryta-water,  or  about  100  c.c. 
of  lime-water.  What  change  do  you  notice  in  the  solu- 
tion ?  A  solid  thus  formed  from  a  clear  solution  by  the 
atldition  of  another  clear  solution,  or  a  gas,  is  called  a  pre- 
cipitate^ because  if  allowed  to  stand  it  would  precipitate, 
or  settle  to  the  bottom.  (If  you  have  both  lime-  and 
baryta-water,  you  can  tell  by  evaporating  equal  quantities 
of  each,  —  a  few  drops,  for  instance,  —  why  more  lime- 
water  is  necessary  than  baryta- water.)  Filter  through  a 
small  filter-paper  so  as  to  obtain  the  precipitate  on  the 
paper.  Transfer  tliis  paper  to  a  small  test-tube  and  pour 
upon  it  a  few  drops  of  liydrochloric  acid.  When  bubbles 
of  gas  are  set  free  as  in  this  case,  the  substance  is  said  to 
effervesce^  or  effervescence  is  said  to  take  place.  Into  the 
test-tube  put  a  burning  match.  Does  it  go  out,  or  does 
it  continue  to  burn  ?  In  the  mouth  of  the  test-tube  hokl 
a  glass  rod  on  which  is  a  drop  of  lime-water  or  baryta- 
water.  What  evidence  have  you  that  the  gas  wliich  you 
obtained  by  putting  hydrochloric  acid  on  tlie  precipitate 
is  the  same  as  that  in  the  breath  which  produced  the  pre- 
cipitate ? 

Leave  lime-  or  baryta-wr.ler  open  to  the  air.  Does  it 
turn  cloudy  as  soon    as   when    you    breathe   through   it  ? 


fr 


^1 


CAIiBOy  DIOXIDE  AND  MONOXIDE 


55 


[ENT  25. 

miii'ite.s, 

100  c.c. 

he  solu- 

1  by  the 

)d  a  pre- 

cipitate, 

tiie-  and 

Liantities 

re  lime- 

rough  a 

on  the 

lid  pour 

Jiibbles 

said  to 

nto  the 

or  does 

)e  liold 

baryta- 

ch  you 

cipitate 

he  pre- 

)oes    it 
gh   it? 


V 


What  does  your  result  prove  about  the  rehitive  quantity 
of  the  gas  in  the  air,  and  in  tlie  breath  when  it  comes 
from  the  body  ?  What  two  elements  did  we  find  are 
contained  in  this  gas?  See  page  31.  Which  of  them  is 
supplied  by  the  air  ?  Where  did  the  other  element  come 
from  in  the  experiment  that  you  have  just  performed  ? 

When  we  breathe,  part  of  our  tissues  are  burned,  but 
the  burning  is  slow  and  the  temperature  is  not  high.  In 
fever,  the  burning  is  more  rapid,  and  the  temperature  rises. 
When  we  take  violent  exercise,  the  temperature  also  rises 
somewhat,  but  not  as  in  fever,  because  the  heat  is  dimin- 
ished by  the  perspiration  produced. 

Was  the  volume  of  the  precipitate  that  you  have  been 
experimenting  with  so  great  as  that  of  the  gas  ()l)tained 
from  it  ?  When  this  gas  was  first  investigated  by  Black, 
in  1755,  he  called  it  ''•fixed  air,"  because  it  appeared  to  be 
fixed  in  chalk  in  the  solid  state.  Bhick  made  his  experi- 
ments with  chalk.  You  may  use  chalk  or  marble  or  ordi- 
nary limestone. 

Preparation  of  **  Fixed  Air**  and  Experiments  with  the 
Gas.  —  Experiment  26.  Put  a  number  of  small  lumps 
of  marble  (chalk  or  limestone)  into  a  flask  fitted  uj)  as 
for  hydrogen  (page  li>)-  Cover  the  marble  with  water 
and  pour  througli  the  thistle-tube  some  hydrochloric  acid, 
till  you  see  the  gas  coming  off  prett}-  rapidly.  Collecit 
over  water  a  number  of  cylinders  of  the  gas.  Remove 
them  from  the  water,  keeping  tlicin  covered  with  glass 
plates  or  cardboard. 

()l)en  one  cylinder,  mouth  upward,  and  another  mouth 
downward,  and  after  a  minute  thrust  a  burning  taper 
into  the  two  cylinders.  What  does  this  experiment  prove 
about  the  weight  of  tixed  air  as  compared  with  that  of 


56 


CHEMISTRY 


atmospheric  air  ?  Light  the  taper  again  and  put  it  into 
the  cylinder  in  which  it  was  extinguished.  Notice  this 
time  whether  the  taper  is  completely  extinguished  or 
whether  the  wick  is  left  glowing. 

Siphon  the  fixed  air  from  another  cylinder  and  let  the 
gas  as  it  comes  out  of  the  siphon  flow  upon  tlie  flame  of 
a  candle.  What  happens  to  the  candle?  The  siphon  of 
the  gas  needs  to  be  started  just  as  a  siplion  of  water  would 
need  to  be  started,  and  this  may  easily  be  done  by  sucking 
the  air  out  of  the  tube.  When  doing  so  you  will  learn 
the  taste  of  the  gas.  What  reason  have  you  for  tliinking 
that  "  soda  water "  may  contain  fixed  air  ?  If  it  does, 
what  reason  have  you  for  considering  that  more  fixed  air 
can  be  dissolved  in  the  water  in  tlie  bottle  where  it  is 
under  pressure,  than  can  be  dissolved  in  water  open  to 
the  air  ? 

Fixed  air  is  sometimes  produced  in  old  wells,  and  as 
the  gas  is  poisonous,  such  wells  are  tested,  if  one  wishes 
to  go  down  into  them,  by  lowering  a  lighted  candle  to  the 
bottom.     How  is  this  a  test  ? 

Half  fill  another  cylinder  of  the  gas  with  water,  cover 
air-tight  with  the  hand,  and  shake  vigorously  for  a  minute 
or  two.  Have  you  any  evidence  from  the  feeling  of  your 
hand  that  the  gas  has  been  partly  absorbed  by  the  water  ? 
Put  the  mouth  of  the  cylinder  under  water  in  the  pneu- 
matic trough  and  remove  your  hand.  What  evidence  have 
you  now  that  the  gas  was  dissolved  to  s  )me  extent  in  the 
water  ? 

Place  a  piece  of  both  red  and  blue  litmus-paper  in  a 
cylinder  of  fixed  air.     Is  it  acid,  alkaline,  or  neutral  ? 

In  addition  to  fixed  air  there  is  another  compound  of  oxy- 
gen and  carbon.     Since  the  proportion  of  oxygen  to  carbon 


i 


in| 

is 


i 


CARBON  DIOXIDE  AND  MONOXIDE 


67 


t  it  into 
:ice  this 
shed   or 

[  let  the 
flame  of 
iphon  of 
r  would 
sucking 
ill  learn 
hinking 
it  does, 
ixed  air 
!re  it  is 
open  to 

and  as 
I  wishes 
3  to  the 

cover 

minute 

of  your 

water  ? 

pneu- 

e  have 

in  the 

r   in  a 
1? 

uf  oxy- 
arbon 


^ 


in  fixed  air  is  twice  that  in  the  other  compound,  the  former 
is  carbon  dioxide  and  the  latter  carbon  monoxide. 

Carbon  Monoxide 

Laboratory  Method  of  Preparation  of  Carbon  Monoxide  and 
Experiments  with  the  Gas. — If  carbon  dioxide  is  passed 
over  red-hot  iron,  it  loses  some  of  its  oxygen  and  becomes 
carbon  monoxide,  while  an  oxide  of  iron  is  formed,  just  as 


Fig.  23 

when  steam  is  passed  over  red-hot  iron.  A  method  of 
operation  which  might  be  used  is  shown  in  Fig.  23.  The 
volume  of  the  monoxide  is  equal  to  that  of  the  dioxide 
from  which  it  was  obtained.  When  carbon  monoxide  is 
required  in  the  laboratory  it  is  not  usually  prepared  in  this 
way,  but  by  heating  oxalic  acid  witli  strong  sulphuric  acid. 
Oxalic  acid  is  a  solid,  composed  of  car])on,  oxyofen,  and 
hydrogen,  in  such  proportions  as  to  form  water,  carbon 
monoxide,  and  carbon  dioxide  ;  and  all  it  needs  is  to  \'f^, 
broken  up  '  i  the  right  way,  in  order  to  obtain  these  three. 
Strong  su"  uric  acid  has  such  a  great  affinity  for  water 
that  whe.i  put  on  many  substances  that  seem  quite  dry,  but 


I 


68 


CHEMISTRY 


that  contain  hydrogen  and  oxygen,  it  abstracts  water  from 
the  compound.  The  chemical  reaction  is  probably  more 
complex  than  here  indicated,  but  for  our  purpose  we  may 
rest  content  with  the  above  ex2)lanation.  T\\iifact  is,  that 
when  oxalic  acid  is  heated  with  strong  sulphuric  acid,  the 
latter  becomes  diluted  with  water,  and  equal  volumes  of 
carbon  monoxide  and  carbon  dioxide  are  set  free. 

ExPEiiiMENT  27.  Into  a  half-litre  flask  fitted  with  a 
thistle-tube  and  a  delivery-tube,  i)ut  about  20  grammes 
of  oxalic  acid  and  cover  it  with  strong  sulphuric  acid. 
Place  the  flask  on  wire  gauze  on  the  ring  of  a  retort  stand. 
Arrange  two  ivash  bottles  half  fdled  with  a  solution  of 
caustic  potash,  so  that  they  may  be  connected  with  the 
delivery-tube  of  the  flask.  In  one  form  of  wash  ))ottle, 
the  bottle  is  fitted  with  two  tubes,  the  longer  of  which  dips 
beneath  the  surface  of  the  liquid  in  the  bottle  and  serves 
to  bring  the  gas  from  the  generating  apparatus  while  the 
shorter  tube  is  well  removed  from  the  liquid  and  serves  as 
a  means  of  escape  for  the  gas  after  its  impurity  has  been 
absorbed  by  the  liquid.  Two  wash  bottles  are  used,  lest 
one  should  not  absorb  all  of  the  impurity.  (Figure  24  shows 
sncli  an  apparatus.)  lleat  the  flask  gently,  moving  the 
flame  about  under  it.  How  can  you  tell  when  the  gas 
l)ecfins  to  come  off?  When  vou  think  that  there  is  some 
escaping  from  the  delivery-tube,  hold  a  roi'l  with  a  drop  of 
lime-water  or  baryta-water  on  it  in  the  stream  of  tfie  escap- 
ing Gfas.  What  chauGre  is  there  in  the  Ihne-water  ?  What 
does  tliis  show?  Be  careful  not  to  iiiliale  much  of  the 
escaping  gases.  Now  join  up  the  flask  with  the  wash 
bottles  [)laced  so  that  the  gas  j^asses  tlirough  one  and  then 
through  the  other.  Tlie  gas  which  escapes  from  the 
second  wash  bottle  can  l)e  collected  in  cylinders  over  water 


^ 


CARBON  DIOXIDE  AXD  MONOXIDE 


59 


jr  from 
y  more 
.ve  may- 
is,  that 
nd,  the 
imes  of 

with  a 

[•ammes 

c  acid. 

;  stand. 

tion  of 

ith  the 

bottle, 

icli  dips 

I  serves 

lile  the 

?rves  as 

IS  been 

ed,  lest 

shows 

ng  the 

le  gas 

Us  some 

Irop  of 

escap- 

What 

of  the 

wash 

id  then 

)m   the 

'  water 


as  usual.  What  is  there  besides  the  liquid  in  the  flask  and 
wash  bottles  when  you  begin  your  experiment  ?  Why  do 
you  not  begin  to  collect  the  gas  at  the  very  first  ?  Before 
you  begin  to  collect  the  gas,  test  what  conies  out  from  the 
wash  bottle  by  a  drop  of  lime-  or  baryta-water.  Does  the 
drop  become  clouded?  What  is  absorbed  by  the  caustic 
potash  solution  ?     Is  the  compound  made  by  the  action  of 


f=^ 


kp- 


(TM^^ 


1  ^ 


/-Vi-ctS      *'  II  u'\ 


Fio.  24 

carbon  dioxide  on  caustic  potash  more  or  less  soluble  than 
the  compound  made  by  the  action  of  carbon  dioxide  on 
caustic  baryta  (baryta- water)  or  lime  ? 

Wlien  water  has  been  kept  back  by  sul])huric  acid,  and 
carbon  dioxide  by  tlie  caustic  potash,  what  is  still  left  to 
collect  in  the  cylinders  ? 

Collect  several  cylinders  of  carbon  monoxide.  To  one 
add  lime  or  ])aryta-water.  If  there  sliould  be  no  precipi- 
tate, apply  a  liglit  to  tlie  gas  in  the  cylinder.  Is  the  gas 
combustible  ?     Is  it  a  supporter  of  combustion  ? 

If  the  gas  burns,  notice  the  colour  of  tlie  flame,  and  when 


60 


CHEMISTRY 


it  goes  out,  shake  up  the  lime-water  in  the  cylinder  and  see 
if  it  becomes  cloudy.  What  does  carbon  monoxide  pro- 
duce when  it  burns  in  air  ?  If  you  got  a  precipitate  when 
you  first  put  in  the  lime-water,  you  should  pour  some  caus- 
tic soda  or  potash  into  the  cylinder,  sliake  it  up  thoroughly 
with  the  gas,  and  transfer  in  the  pneumatic  trough  to 
another  cylinder  and  do  the  experiment  as  already  de- 
scribed. 

If  you  have  a  store  of  oxygen,  fill  a  cylinder  one-third 
svith  oxygen  and  then  add  carbon  monoxide  till  the  cylin- 
der is  full  of  gas.  Remove  the  cylinder  and  carefully 
apply  a  lighted  taper.  You  sliould  have  a  violent  explo- 
sion. Instead  of  oxygen  you  may  use  air,  filling  five- 
sevenths  of  the  cylinder  with  air  and  two-sevenths  with 
carbon  monoxide.  The  tube  b  in  the  figure  contains  cop- 
per oxide  which  is  supposed  to  be  heated  while  carbon 
monoxide  is  passed  over  it.  What  liquid  is  supposed  to 
be  in  the  bottle,  and  what  does  the  experiment  show  ? 

Shake  up  carbon  monoxide  with  water  as  you  did  carbon 
dioxide.     Is  it  more  or  less  soluble  ? 

Statement  of  Occurrence  and  Properties  of  Carbon  Dioxide 
and  Carbon  Monoxide.  —  It  will  be  convenient  to  discuss 
carbon  dioxide  and  carbon  monoxide  together,  comparing 
and  contrasting  them. 

Since  carbon  monoxide  burns  in  air,  it  is  natural  to 
suppose  that  there  would  not  be  much  of  it  found  free 
in  the  atmosphere.  On  tlie  other  hand,  carbon  dioxide 
is  produced  when  all  ordinary  fuels  burn  and  when  all 
animals  breathe,  and  so  naturally  exists  in  the  atmosphere 
at  all  times,  There  are  about  four  volumes  of  carbon 
dioxide  in  ten  thousand  volumes  of  air,  and  there  would 
be  a  larger  amount  but  that  plants  decompose  it,  taking 


I 


I 


CARBON  DIOXIDE  AXD  MOXOXIDE 


61 


in  carbon  dioxide  and  sending  out  oxygen  in  somewhat 
the  same  way  as  animals  inhale  oxvcren  and  exhale  carbon 
dioxide. 

Carbon  dioxide  may  be  said  to  be  found  ready  made  in 
marble,  chalk,  and  other  kinds  of  limestone,  and  if  these 
are  heated  strongly  enough,  carbon  dioxide  is  <]^iven  off 
and  lime  is  left  behind.  It  is  in  this  way  that  ordinary 
quicklime  is  made.  Some  other  minerals  contain  carbon 
dioxide,  but  limestone  is  the  most  important. 

Of  the  proper  'es  of  carbon  monoxide  and  carbon  dioxide 
you  know  someilr  g.  They  are  both  colourless;  carbon 
monoxide  has  .ittie  odour  or  taste,  but  [)roduces  a  very 
disagreeable  sensation,  resembling  an  odour  and  taste. 
Carbon  dioxide  has  a  slightly  acid,  pleasant  taste  and  a 
slight  odoui,.  Both  gases  are  usually  spoken  of  as  very 
poisonous,  but  they  act  in  different  ways.  The  blood  is 
not  a  homogeneous  liquid,  that  is,  is  not  vuiiform.  The 
redness  is  caused  by  small  red  bodies  called  red  corpuscles 
floating  in  an  almost  colourless  liquid.  The  red  cor- 
puscles contain  a  substance  which  takes  up  oxygen  when 
blood  passes  through  the  lungs.  The  blood  in  this  way 
becomes  a  brighter  red.  As  it  passes  through  the  blood- 
vessels, tlie  oxygen  is  given  up  to  the  tissues.  Carbon 
dioxide  is  produced  and  is  partly  dissolved  in  the  colour- 
less portion  of  the  blood,  and  partly  loosely  combined  with 
the  red  corpuscles,  which  become  dark  in  colour.  As  the 
blood  passes  through  the  lungs  again,  the  carbon  dioxide 
escapes  from  it  and  more  oxygen  is  taken  in.  If  an  animal 
inhales  too  much  carbon  dioxide  with  the  air,  the  carbon 
dioxide  of  the  blood  cannot  escape  from  the  lungs  and  so 
is  carried  along  in  the  blood,  and  death  will  soon  follow 
unless  the  animal  is  removed  from  the  atmosphere  contain- 


02 


CHEMISTRY 


in^  the  excess  of  carbon  dioxide  and  put  into  an  atmosphere 
witli  plenty  of  good  oxygen,  in  which  case  it  will  prob- 
ably recover  in  a  sliort  time  and  sulTer  no  serious  effects. 
There  is  a  place  in  Italy  where  this  experiment  is  said 
to  be  often  performed.  It  is  called  the  (jrotto  del  Cano, 
because  (the  carbon  dioxide  being  near  the  ground)  dogs 
witli  tlieir  noses  close  to  the  earth  are  suffocated,  while 
people  can  walk  along  uninjured,  their  heads  being  above 
the  poisonous  gas.  Visitors  are  shown  the  experiment  of 
leaving  a  dog  in  tlie  grotto  till  he  becomes  insensible,  and 
bringing  him  out  in  time  to  revive  him.  The  action  of 
carbon  dioxide  is  tlierefore  rather  suffocating  than  poison- 
ous. An  investigatcji'  has  stated  that,  provided  a  sulHcient 
amount  of  oxygen  is  contained  in  the  air,  the  presence  of 
carbon  dioxide  is  not  injurious.  Carbon  dioxide  from  the 
breath  contains  organic  matters  that  are  hurtful  and 
mu-st  be  removed,  and  it  is  said  to  be  owing  to  their  pres- 
ence and  to  the  diminution  of  oxygen  that  headache  and 
other  poisonous  effects  have  been  attributed  to  carbon 
dioxide.  Physiologists  are  not  agreed  on  the  matter, 
w^hich  needs  further  investigation. 

The  poisonous  action  of  carbon  monoxide  is  more  serious. 
Carbon  monoxide  forms  a  compound  with  the  part  of  the 
red  corpuscles  that  sliould  be  oxidised  by  the  air,  and  thus 
prevents  the  action  of  the  oxygen.  The  compound  is 
very  firm,  so  that  if  an  animal  is  taken  out  of  an  atmos- 
phere of  carbon  monoxide  into  the  air,  the  oxygen  still 
cannot  act  on  these  corpuscles,  and  the  only  chance  of 
recovery  is  tliat  there  are  enough  corpuscles  unacted  upon 
to  carry  on  the  processes  of  life.  An  atmosphere  of  pure 
oxygen  is  more  effective  than  air  in  its  action  on  the 
blood,  and  is  thus  to  a  certain  extent  an  antidote  to  poi- 


I 


('Annoy  dioxide  axd  moxoxidI': 


68 


osphere 
i  pi'ob- 
effects. 
is  said 
I  Cano, 
I )  dogs 
,  while 
^  above 
neiit  of 
»le,  and 
ition  of 
poison- 
IHcient 
ence  of 
om  the 
111  and 
r  pres- 
he  and 
carbon 
natter, 

erious. 
of  the 
d  thus 
ind  is 
itmos- 
n  still 
nee  of 
upon 
pure 
n  the 
0  poi- 


soning l)y  carbon  monoxidi'.  Carbon  monoxide  is  by  far 
the  more  dangerous  of  the  two  gases,  and  it  is  nearly 
always  produced  to  some  extent  where  coal  is  burned  (the 
blue  flames  seen  in  coal  lires  being  due  to  its  coMd)us- 
tion).  It  is  said  that  red-hot  iron  allows  the  gas  to  pass 
through  it,  and  that  therefore  red-hot  stoves  are  mi- 
healthy,  but  it  is  possible  that  the  bad  effects  of  hot 
stoves  are  due  to  other  causes. 

Carbon  monoxide  is  slightly  lighter  than  air,  being  of 
the  same  density  as  nitrogen,  while  carbon  dioxide  is  about 
one  and  a  half  times  as  heavy  as  air. 

Carbon  dioxide  at  the  ordinary  temperature  is  dissolved 
by  about  its  own  volume  of  water,  while  carbon  monoxide 
is,  like  hydrogen  and  oxygen,  very  slightly  soluble. 

Carbon  dioxide  is,  as  might  be  ex})e(;te(l,  tlie  more 
easily  condensed,  Ijecoming  licpiid  at  15°  C.  when  sub- 
jected to  a  pressure  of  fifty-two  atin()S[)heres  and  liquefy- 
ing at  ordinary  pressure  if  cooled  below  —  80°  ( -.  Carbon 
monoxide  is  not  liquefied  at  all  at  the  ordinary  tempera- 
ture, no  matter  what  pressure  is  employed.  When  liquetied 
by  very  intense  cold  the  liquid  boils  at  —  11)0°  C,  which 
is  almost  the  same  temperature  as  that  at  which  nitrogen 
boils. 

The  chemical  properties  of  the  two  gases  are  very  differ- 
ent. Carbon  monoxide  burns  in  air,  to  form  carbon 
dioxide,  while  naturally  the  latter  does  not  burn  in  air,  else 
it  would  not  be  the  product  of  the  coml)Usti{)n  of  the 
monoxide.  Carbon  dioxide  combines  with  alkalis  in  aque- 
ous solution,  whereas  carbon  monoxide  does  not.  Liquid 
carbon  dioxide  is  sold  in  strong  iron  cylinders,  and  is 
used,  among  other  things,  for  making  soda  water. 


CHAPTER   VI 


ACTION   OF  HYDROCHLORIC  ACID  ON  ALKALIS 

Formation    of    Hydrochloric    Acid.  —  Eximckiment  28. 

Test  whether  common  suit  is  ueid,  alkaline,  or  neutral. 
Put  a  little  salt  into  a  test-tn})e,  pour  on  it  a  few  drops  of 
strong  sulphuric  jicid,  and  heat  gently.  What  happens? 
Put  a  piece  of  moist  litmus-paper  into  the  mouth  of  the 
test-tube  without  allowing  it  to  touch  the  sides,  lest  it 
should  get  a  little  of  the  sulphuric  acid  on  it.  Is  there 
any  indication  that  a  gas  is  coming  off?  If  so,  is  it  acid, 
alkaline,  or  neutral?  In  another  test-tube  heat  some  sul- 
phuric acid  alone.  In  neither  case  should  the  test-tube 
be  heated  so  strongly  that  you  cannot  keep  your  hand  on 
the  heated  part  when  you  remove  it  from  the  flame.  Is 
there  any  effect  on  the  litmus-paper  held  at  the  mouth  of 
the  test-tube  containing  sulphuric  acid  alone  ?  Does  sul- 
phuric acid  volatilise  at  the  temperature  which  you  have 
used  ?  What  evidence  is  there  that  when  sulphuric  acid 
is  put  upon  the  neutral  substance,  salt,  an  acid  different 
from  sulphuric  acid  is  produced? 

The  substance  formed  by  the  action  of  oil  of  itriol 
(sulphuric  acid)  on  common  salt  was  once  called  "  spirits 
of  salt."  It  is  now  called  hydrochloric  acid.  Hola  a 
glass  rod,  with  a  drop  of  water  on  it,  in  the  mouth  of  the 
test-tube  in  which  hydrochloric  acid  is  being  produced. 
After  a  few  seconds,  taste  the  drop.  What  evidence  have 
you  that  water  dissolves  spirits  of   salt?      What  effect 

64 


f 


ACrioy    OF  UVDROCHLOiUC  ACID   O.V    ALKALIS     ()5 


NT    28. 

leutral. 
rops  of 
ppens  ? 
of  the 
lest  it 
s  there 
it  acid, 
ne  siil- 
st-tube 
md  oil 
le.  Is 
)uth  of 
es  sul- 
Li  have 
ic  acid 
fferent 

itriol 
spirits 
Toki  a 
of  the 
iuced. 
e  have 

effect 


would  you  expect  a  drop  of  the  solution  to  have  on  litmus- 
paper?  You  remeiuber  that  the  volatile  alkali  ainnioiiia 
was  produced  by  the  action  of  a  lixed  alkali,  lime,  on  a 
salt,  sal-ammoniac.  Is  sulphuric  acid  or  hydrochloric  acid 
the  more  volatile?  There  are  very  few  volatile  alkalis 
in  comuKm  use,  but  there  are  a  numl)er  of  volatile  acids. 
VVliat  hint  have  you  of  a  possible  method  for  j^^'tting  a 
volatile  acid  from  a  salt?  It  is  not  well  to  jump  too  rap- 
idly to  conclusions  ;  but  whenever  you  are  in  doubt  as  to 
how  to  produce  an  acid  from  a  salt,  you  should  rcmendjcr 
how  hydrochloric  acid  is  obtained  from  connnon  salt,  and 
consider  whether  there  is  any  objection  to  using  a  similar 
method  for  the  acid  whicii  you  wish  to  obtain. 

There  are  many  properties  of  hydrochloric  acid  that  we 
shall  have  to  consider  later,  but  just  now  we  shall  investi- 
gate the  action  of  hydrochloric  acid  on  alkalis  such  as 
caustic  soda  and  caustic  potash. 

Addition  of  Hydrochloric  Acid  to  Caustic  Soda.  —  Ex- 
periment 29.  Into  a  porcelain  evaporating  dish  put  a 
piece  of  caustic  soda  about  the  size  of  a  small  bean. 
Pour  on  it  two  or  three  times  its  own  volume  of  water 
and  allow  it  to  dissolve.  What  change  do  you  notice  in 
the  temperature  ?  Now  very  carefully  add  a  few  drops  of 
strong  hydrochloric  acid  solution,  allowing  it  to  run  down 
the  side  of  the  dish,  not  pouring  it  directly  on  the  caustic 
soda.  What  evidence  have  you  that  the  hydrochloric  acid 
and  the  caustic  soda  act  very  energetically  on  each  othei*? 
Continue  adding  hydrochloric  acid  till  there  is  no  further 
action.  What  evidence  have  you  that  hydrochloric  acid 
has  made  the  substance  less  oluble?  Evaporate  till  the 
solid  is  perfectly  dry.  Is  the  .ibstance  left  behind  caustic 
soda?     What  does  the  residue  after  evaporation  (the  sub- 


66 


CUEMISTBY 


i 


stance  left  behind  when  all  the  liquid  was  evaporated) 
taste  like? 

An  experiment  such  as  you  have  now  performed  is 
called  a  qualitative  experiment,  because  you  have  examined 
the  qualities  of  the  substances  used  and  the  substance  pro- 
duced. You  have  taken  no  particular  care  about  quanti- 
ties. But  in  chemistry  it  is  often  very  important  to  know 
something  about  quantities,  and  our  knowledge  is  very 
imperfect  unless  we  have  such  informaticm.  Let  us  en- 
deavour to  find  out  whether  there  is  any  detiniteness 
about  the   (piantity   of    hydrochloric    a(;id  which  can   be 

used  up  by  a  given  amount 
of  caustic  soda,  or  whether 
the  quantity  varies. 

Quantitative  Experiments 
with  Caustic  Soda  and  Hydro- 
chloric Acid ;  Burettes.  — 
Experiment  30.  Dissolve  4 
grammes  of  caustic  soda  in 
200  c.c.  of  w^ater  and  stir 
so  that  the  solution  will  be 
uniform.  In  anotlier  vessel 
mix  thoroughly  25  c.c.  of 
strong  hydrochloric  acid 
solution  and  375  c.c.  of 
water,  'riioroughly  clean  a 
burette  (a  graduated  glass 
tube  such  as  those  repre- 
sented in  Fig.  25).  The  burette  must  not  be  greasy 
inside,  nor  must  droi)s  renuiin  on  the  walls  wlien  the 
contained  liquid  runs  out.  It  may  be  necessary  to  rinse 
the  tube  with  strong  caustic  soda  solution  or  with  nitric 


Fir..  25 


a 

d 

til 

di 

1< 

eii 

w 

ofl 

th 


;i 


ACTION   OF  IIYDROClILOlilC  A(  ID   OX  ALKALIS     (17 


lorated) 

rmed  is 
[amined 
ice  pro- 
;  quant i- 
:o  know 
is  very 
t  us  eii- 
niteness 
can  be 
amount 
whether 

jriments 

I  Hydro- 

Bttes.  — 

ssolve  4 

soda  in 

nd    stir 

will  be 

vessel 

c.c.    of 

acid 

.c.     of 

lean  a 

glass 

repre- 

greasy 

ni    the 

rinse 

nitric 


acid,  or,  perhaps  still  better,  with  a  solution  of  potassium 
dichromato  and  sulphuric  acid.  It  nuist  linally  be 
tlioroughly  washed  with  water.  Allow  tlic  water  to 
drain  out,  then  i)ut  into  the  burette  a  little  —  about 
10  c.c. — of  the  soda  solution;  let  it  run  from  end  to 
end  of  the  tube  and  drain  out  as  well  as  possible.  Then 
with  the  soda  solution  fdl  the  burette  to  about  the  top 
of  the  graduation  and  clamp  it  in  a  vertical  })osition.  In 
the  same  way  fill  another-  burette  with  liydrochloric  acid 
and  clam[)  it  in  position.  Run  a  little  of  the  litjuid  from 
each  of  tlie  burettes  to  make  sure  that  tlie  little  delivery 
tube  at  the  bottom  is  quite  full  of  licpiid  and  contains 
no  air  bubbles. 

Now  carefully  read  the  burette  containing  the  caustic 
soda.  Reading  the  burette  means  finding  the  position 
of  the  top  of  the  liquid.  When  you  look  at  the  top  of 
the  liquid  you  will  see  that  it  iias  a  curved  surface,  and 
the  best  way  to  read  is  to  find  exactly  at  what  place  you 
see  the  lowest  i)art  of  tliis  curved  surface  (called  the  bot- 
tom of  the  meniscus).  The  burette  is  graduated  from 
the  top,  and  the  burette  you  use  should  Ijc  graduated  in 
c.c,  which  are  numbered,  and  in  tenths  of  a  c.c,  wliiih 
are  indicated  by  short  lines.  Suppose  the  top  of  the 
liquid  is  between  tlie  numbers  1  and  2,  you  look  to  see 
below  which  intermediate  mark  it  is  situated.  You  will 
easily  be  able  to  see  appntximatdy  its  position.  Su[)pose 
it  is  somewhat  below  the  seventli  little  mark,  'i'hcn  tlie 
reading  is  1.7-}-.  liut  you  should  read  it  more  closely, 
and  to  do  so  needs  care.  Viju  nuist  liave  your  eye  on  a 
level  with  the  bottom  of  the  meniscus.  In  order  to  under- 
stand why,  move  your  eye  up  and  down  and  sec  if  the 
reading  appears  to  be  the  same  in  all  positions  of  your 


'i  !■ 


68 


CHEMISTRY 


Fig.  2(J 


eye.      The  figure  (Fig.  20)  illustrates  this  point.      You 
will  [)robcibly  need  something  dark  just  behind  the  burette 

to  enable  vou  to  see 
the  bottom  of  the  me- 
niscus plainly.  You 
may  now  be  able  to 
judge  pretty  nearly 
how  many  tenths  of 
the  distance  between 
the  seventh  and  eighth 
division  it  is.  Supi)ose 
it  is  six-tenths,  the 
reading  is  l.TO.  It  is 
not  very  easy  to  read  quite  so  closely,  so  that  you  may 
be  satisfied  if  you  can  decide  whether  the  reading  is 
nearest  1.7^5,  1.75,  or  1.77.  You  see  now  why  it  is  so 
important  that  none  of  the  liquid  sh  aid  cling  to  the  sides 
of  the  tube  when  the  solution  is  an  out.  You  should 
wait  a  minute  or  so  before  taking  a  reading,  until  all  of 
the  li(iui(l  has  drained  down.  Hun  15  c.c.  of  the  caustic 
soda  solution  intv)  a  porcelain  dish,  add  a  little  litmus  solu- 
tion, and  then  after  carefully  reading  the  hydrochloric 
acid  burette  run  in  the  acid.  What  change  is  there  in 
the  colour  of  the  litmus  just  where  the  acid  strikes  the 
liquid  in  the  dish  ?  Does  this  colour  remain  or  does  it 
vanish '/  What  difference  is  there  in  this  respect  between 
when  you  begin  to  run  in  the  acid  and  after  you  have  run 
in  a  considerable  quantity  ?  You  wish  to  make  the  solu- 
tion just  neutral.  What  indication  have  you  that  you 
should  add  the  hydrochloric  acid  more  slowl}*  after  a 
wliile  than  you  did  at  first  ?  Why  should  you  stir  the 
liquid  and  add  the  acid  drop  by  drop  when  you  come  near 


You 
burette 
to  see 
lie  me- 
You 
ible    to 
nearly 
iths    of 
letween 
eighth 
kippose 
IS,    the 
It  is 
DU  may 
ding   is 
it  is  so 
le  sides 
should 
1  all  of 
caustic 
IS  solu- 
|)chloric 
lliere  in 
kes  the 
does  it 
letween 
Lve  run 
le  solu- 
lat  you 
lifter  a 
Itir  the 
lie  near 


ACTION  OF  HYDROCHLORIC  ACID   0\  ALKALIS     ()0 

the  end?  Each  time  you  add  a  drop,  notice  the  reading 
of  the  burette,  not  very  accurately,  l)ut  so  close  tliat  you 
will  have  r.  pretty  good  idea  how  many  hundredths  of 
a  c.c.  there  are  in  each  drop.  Tlie  size  of  drop  varies 
with  the  burette.  You  will  probably  not  succeed  in  liit- 
ting  the  neutral  point  exactly,  but  will  overshoot  the  mark. 
If,  however,  you  notice  the  reading  of  the  burette  each 
time  you  add  a  drop,  you  will  have  a  pretty  fair  idea  how 
much  you  have  overshot  the  mark.  If,  for  instance,  when 
the  burette  read  20.00  c.c.  the  litmus  was  decidedly  blue, 
and  when  you  have  added  anotiier  drop  you  Hud  tlie  read- 
ing 20.()r)  and  the  litmus  decidedly  red,  you  can  tell  how 
much  acid  is  retpiired  to  within  tiie  limits  of  0.00  c.c, 
and  when  you  try  a  second  time  you  endeavour  to  hit  the 
mark  more  closely. 

Having  found  how  much  acid  is  required  to  neutralise 
15  c.c.  of  caustic  soda,  iind  out  how  much  is  recpiired  for 
20  c.c.  Is  or  is  not  the  (piantity  of  acid  in  tin;  same  ratio 
as  the  quantity  of  soda?  It  may  be  worth  while  to  see 
whether  the  amount  of  acid  required  is  the  same  i" 
dilute  the  caustic  soda  after  putting  it  into  the  dish. 


y 


Weigl 


1  a  sma 


11 


por 


celain  disli,  put  in  20  c.c.  of  caustic 


soda,  and  exac^tly  neutralise  with  hydrochloric  acid.  Then 
evaporate  to  dryness  and  weigh  again.  Wliat  is  the  solid 
residue?       How    much    does    it    weiuh  ?      Take    another 

Id 


a( 


20  c.c.  of  soda  also  in  a  weighed  porcelain  dish, 
considerably  more  acid  than  is  necessary  to  neutralise  it, 
evai)orate  to  dryness,  and  weigh,  ("an  you  get  more  salt, 
or  can  you  not,  l)y  adding  the  larger  (juantity  of  acid? 
Is  the  residue  this  time  alkaline,  neutral,  or  acid  ?  If  you 
hav^  a  given  quantity  of  salt,  would  it  be  possible  for  you 
to  calculate  how  many  c.c.  of  vour  caustic  soda  solution 


*s&. 


■*»'■* 


70 


CllhMJ^'fUY 


4! 


and  of  your  hydL'oc;lik)ric  <u;id  would  be  necessary  to  pro- 
duce it,  or  is  sucli  a  calculation  impossible  ? 

Quantitative  Experiments  with  Caustic  Potash  and 
Hydrochloric  Acid.  —  Expekime:;t  31 .  Dissolve  4  grammes 
of  caustic  potash  in  200  c.c.  of  water.  Every  c.c.  of  the 
solution  will  now  contain  as  much  caustic  potash  as  the 
other  alkaline  solution  contained  of  caustic  soda.  Put 
some  of  the  solution  into  ^  burette.  You  may  use  the 
one  you  had  for  the  soda,  cleaning  it  out  and  rinsing  it 
with  a  little  of  the  potash  solution.  Find  jut  how  much 
hydrochloric  acid  is  required  to  neutralise  15  c.c.  and 
20  c.c.  of  this  solution.  Is  the  amount  of  acid  in  the 
same  ratio  as  the  quantity  of  caustic  potash  solution? 
Does  it  require  exactly  tlio  same  amount  of  hydrocldoric 
acid  to  neutralise  20  c.c.  of  caustic  potash  as  of  caustic 
soda?  If  noi  vhat  is  the  ratio  between  the  amounts? 
Take  20  c.c.  of  caustic  potash  in  a  weighed  porcelain  dish, 
neutralise,  eva])orate  to  dryness,  and  weigh.  Take  an- 
other 20  c.c.  of  potash,  add  much  more  than  enougli  acid 
to  iVv  . .  alise,  eva[)orate  to  dr3^ness,  and  weigh.  How  do 
the  V  '  i^hts  compare?  Wliat  happens  to  the  extra  acid 
that  was  added  in  the  second  case  ?  Is  the  weight  of  the 
salt  obtained  from  20  c.c.  of  the  caustic  potash  solution 
equal  to,  less  tlian,  or  greater  than  the  weight  of  the  salt 
obtained  from  20  c.c.  of  tlie  caustic  soda  solution  ? 

The  experiments  that  you  have  done  should  enable  you 
to  answer  the  following  question  ;  but  if  not,  you  had 
better  try  the  direct  experiment.  Will  20  c.c.  of  hydro- 
chloric acid  need  a  greater  or  less  weight  of  caustic  potash 
than  of  caustic  soda  exactly  to  neutralise  it  ?  Is  the 
weight  of  caustic  potasli,  equivalent  to  a  given  weight  of 
hydrochloric  a<!id,  greater  or  Jess  than  the  Aveight  of  caustic 


■■4^^. 


ACTION  OF  urnnoriiLoiii    ac'id  ox  alkalis    71 


to  pro- 

sh    and 

grammes 

:.  of  the 

li  as  the 

[a.     Put 

use  the 

using  it 

iw  much 

c.c.  and 

I  in  the 

olution  ? 

•ocliloric 

:  caustic 

mounts  ? 

ain  dish, 

'ake   an- 

igli  acid 

low  do 

:i'a  acid 

of  the 

solution 

the  salt 


soda,  equivalent  to  the  same  given  \:-Agh-  of  hydrochloric 
acid?  This  question  is  frequently  put  in  the  shorter 
form:  Is  tlie  equivalent  of  caustic  potash  greater  or  less 
than  the  equivalent  of  caustic  soda  ? 

If  other  acids  were  used  instead  of  hydrochloric  acid, 
corresponding  experiments  might  be  carried  out. 


f^ 


d)le  you 
^'ou  had 
hydro- 
potash 
Is  the 
eight  of 
caustic 


CHAPTKR   Vll 


qi 


LAWS  OF  CHEMICAL  COMBINATION  AND  THE  ATOMIC  THEORY 

Yor  have  now  become  acquainted  witli  a  number  of 
chemical  substances,  having  passed  from  very  familiar 
ones  to  others  not  so  commonly  known.  You  have  ob- 
tained a  few  (quantitative  results,  and  in  some  cases  when 
you  did  not  yourself  perform  the  experiment  you  were 
told  what  has  been  proved  experimentally  by  others. 

Quantitative  Results  Recapitulated.  —  Water  consists  of 
hydrog'^u  and  oxygen,  the  volume  of  the  hydrogen  being 
twice  tiiat  of  the  oxvufcn,  wliile  on  the  other  hand  the 
weight  of  tlie  oxygen  is  eight  times  that  of  the  hydrogen. 

Tlie  zinc  used  for  making  hydrogen  is  approximately 
six-tentlis  the  weight  of  the  strong  sulphuric  acid  required. 
The  weiglit  of  potassium  chloride  obtained  by  heating 
potassium  chlorate  is  ap[)roximately  six-tenths  that  of  the 
chlorate.  Ozone  is  one  and  one-half  times  as  heavy  as 
the  same  volume  of  oxygen.  Ammonia  is  composed  of 
h^'drogen  and  nitrogen,  the  volume  of  hydrogen  being 
three  times  that  of  the  nitrogen,  while  the  weights  are  in 
the  ratio  of  3  to  14.  Carbon  dioxide  has  twice  the  quan- 
tity of  oxygen  for  a  given  amount  of  carbon  that  carbon 
monoxide  lias.  The  quantities  of  hydrochloric  acid  needed 
to  neutralise  soda  and  pi)tash  you  have  investigated  pretty 
thorouglily 

Another   experiment,  in    which   considerable   accuracy 

72 


P^ 


LAWS   OF  CHEMICAL   COMIUXATIOX 


73 


rHEORY 

iber  of 
ainiliar 
ive  ob- 
s  when 
u  were 
s. 

sists  of 

1  being 

nd  the 

rogen. 

niately 

|uired. 

1  eating 

of  the 

avy  as 

sed  of 

being 

lire  in 

quan- 

arbon 

leeded 

pretty 

:uracy 


may  be  attained,  will  give  you  further  confidence  in  tlie 
quantitative  results  of  chemistry. 

Quantitative  Experiment ;  Experimental  Errors. — Kx- 
PERIMKNT  32.  Weigh  carefully  about  2  gi-anmics  of  [)er- 
fectly  dry  potassium  chlorate.  It  is  necessary  tliat  you 
should  note  exactly  the  weight,  but  not  tliat  it  should  l)e 
exactly  2  grammes.  Mix  it  with  id)()ut  half  its  weight  of 
perfectly  dry  manganese  dioxide  ;  introduce  the  mixture 
into  a  dry  test-tube  and  weigh.  Heat  the  mixture  until 
all  of  the  oxygen  in  the  chlorate  is  given  off.  When  the 
tube  is  cool,  weigh  it  again.  To  what  is  the  loss  of  weigid 
due?     Why  was  it  so  necessary  to  have  everything  dry  .' 

There  are  always  errors  in  carrying  out  an  exi)eriment, 
errors  called  experimental  errors.  The  amount  of  error  is 
in  some  cases  small,  if  the  experiment  is  easy  and  tlie 
experimenter  is  very  careful.  In  some  cases  the  experi- 
mental error  is  large.  In  tlie  al)ove  experiment  one 
member  of  a  class  experimenting  might  weigh  the  chlorate 
inexactly,  another  might  lose  a  little  of  it  after  it  was 
weighed,  a  third  might  not  have  had  it  perfectly  dry, 
a  fourth  might  not  heat  till  all  of  the  oxygen  was  driven 
off,  a  fifth  might  have  a  little  of  the  mixture  tlirown  out  of 
the  tubes  by  the  oxygen  coming  off  rapidly,  and  a  nundjcr 
of  other  errors  might  occur.  Some  of  the  errors  miglit 
make  the  amount  of  oxygen  a[)[)ear  greater  than  it  should, 
others  would  make  it  appear  less.  liut  if  the  average  of 
the  results  obtained  by  ten  or  a  dozen  experimenters,  who 
had  exercised  a  reasonable  amount  of  care,  were  taken,  the 
probability  is  that  the  result  would  not  be  far  wrong. 
In  this  case  the  amount  of  oxygen  should  ])e  nearly 
30.2%  of  the  original  chlorate.  What  will  be  the  amount 
of  chloride  left  ? 


74 


L'UEMISrUY 


The  Law  of  Definite  Proportions.  —  Your  exporimcnts 
have  gone  a  certain  distance  to  i)rove  tliat  a  chemical 
compound  always  has  tlie  same  composition.  One  sam2)le 
of  potassium  chlorate  docs  not  c(jntain  J50,2'/^  of  oxygen, 
and  another  sample  41%.  A  certain  amount  of  common 
salt  is  not  made  to-day  from  10  grammes  of  caustic  soda, 
and  to-morrow  from  10.. 5  grammes. 

Tlu!  statement  that  the  composition  of  com})ounds  is 
invarial)lc  or  always  tlie  same  is  usnally  called  the  first 
chemical  law,  or  The  Law  of  Definite  Proportions.  Between 
tlie  years  1790  and  ISOU  there  was  a  great  controversy, 
chiefly  hetween  two  French  chemists,  as  to  whether  this 
statement  were  true,  so  that  it  has  been  very  carefully 
tested. 

The  Law  of  Multiple  Proportions.  —  You  found  that 
there  are  two  oxides  of  carbon,  —  carbon  monoxide  and 
carbon  dioxide.  Carbon  monoxide  contains  57.14%  of 
oxygen  and  42.80%  of  carbon.  Carbon  dioxide  contains 
72.78%  of  oxygen  and  27.27%  of  carbon,  that  is,  42.86 
grammes  of  carbon  are  combined  with  57.14  grammes  of 
oxygen  in  carbon  monoxide,  and  27.27  grammes  of  car- 
bon are  combined  with  72.73  grammes  of  oxygen  in  carbon 
dioxide.  If  the  calculation  be  made,  it  will  be  seen  that 
in  carl)on  monoxide  1  gramme  of  carbon  is  united  to  1.83 
grammes  of  oxygen,  and  in  carbon  dioxide  1  gramme  of 
carbon  is  united  to  2.66  grammes  of  oxygen. 

Dalton  described  several  cases  like  this,  between  the 
years  1803  and  1807,  and  he  made  tiie  statement  that  is 
often  called  the  second  chemical  laAv,  or  The  Law  of  Multi- 
ple Proportions.  This  statement  is  that  when  two  elements 
combine  with  each  other  in  more  than  one  proportion  by 
weight,  the  quantities  of  one  of  the  elements  which  com- 


bil 
titi 
otl 
wi| 

thii 

Til 

to 

wii 

wil 


LAWS   OF  CUKMICAL   ('OMIU\ATrjy 


n  the 
lat  is 

[ulti- 
Ineiits 

)!!  by 
K)in- 


bine  to  form  two  or  more  compounds  witli  a  given  quan- 
tity of  tlie  otlier  element  stand  in  sim[)le  relations  to  each 
otlier.  For  instance,  a  given  (quantity  of  cari)()n  unites 
witli  a  certain  definite  quantity  of  oxygen  or  witli  twice 
that  quantity,  and  not  with  lJ)8r)4  times  that  ([uantity. 
There  is  a  sudden  jump  from  the  given  amount  of  oxygen 
to  double  that  amount.  In  the  same  way  hydrogen  unites 
with  eight  times  its  weight  of  oxygen  to  form  water,  and 
with  sixteen  times  its  weight  to  form  hydrogen  })eroxide. 
We  found  that  there  are  two  oxides  of  iron  —  one,  red 
hematite,  which  is  non-magnetic,  and  anotlier  which  is 
magnetic.  The  ox^'gen  is  not  twice  as  much  in  one  case 
as  in  the  otlier,  but  the  proportions  are  simple. 

The  amount  of  oxygen  in  the  air  varies  between  the 
limits  20.84%  and  20.91)%  l)y  volume.  Is  it  probable  that 
air  is  a  mixture  of  oxygen  and  nitrogen,  or  a  com[)ound? 

The  Atomic  Theory;  Dalton*s  Symbols.  —  Dalton  set  him- 
self to  devise  some  theory  to  account  for  the  fact  that  ele- 
ments unite  in  this  simple  way,  that  a  compound  is  always 
of  a  definite  composition,  and  that  elements  do  not  unite 
in  haphazard  proportions.  lie  suggested  the  atomic 
theory.  This  theory  is  that  all  substances  are  made  up 
of  innumerable  small  indivisible  particles,  called  atoms 
(from  the  (ireek  word  meaning  incapable  of  being  cut). 
These  particles  are  far  too  small  to  be  visible  through  a 
microscope.  We  do  not  know  their  shape,  and  our  know- 
ledge of  their  size  and  weight  is  very  vague.  In  the  case 
of  elements  all  the  atoms  are  alike  ;  compounds  are  made 
up  of  different  kinds  of  atoms.  Though  we  do  not  know 
the  actual  weight  of  the  atoms,  we  know  the  ratio  between 
the  weights  of  the  different  kinds  of  atoms. 

Dalton  used  certain  symbols  to  represent  atoms  of  dif- 


76 


CHEMISTRY 


ferent  elements,  and  when  lie  wished  to  represent  a  com- 
pound he  put  the  proper  syml)()ls  together.  Oxygen  was 
represented  by  the  symbol  Oi  hydrogen  by  O,  nitrogen 
by  0,  (.'ur])on  by  ••  (Aiibon  monoxide  was  represented 
by  putting  the  symbol  for  one  atom  of  carbon  Ixjsidt  that 
for  one  atom  of  oxygen,  tluis,  •O-.  while  carbon  dioxide 
was  re[)resented  thus,  0#0. 

It  is  easily  seen  that  the  smallest  possible  quantity  of 
carbon  monoxide  would  consist  of  one  atom  of  carbon  and 
one  atom  of  oxygen,  for  this  amount  of  carbon  monoxide 
could  not  be  divided  witliout  breaking  up  the  substance 
into  its  elements.  It  would  be  im[)ossible  to  add  oxygen 
to  this  smallest  quantity  of  carbon  monoxide  except  by 
adding  one  or  more  atoms  of  oxygen.  One  atom  of  oxy- 
gen can,  in  fact,  be  added,  forming  carbon  dioxide  ;  and 
the  smallest  quantity  of  carbon  dioxide  contains  two 
atoms  of  oxygen  for  one  of  carbon.  Any  large  quantity 
of  carbon  monoxide  or  of  carbon  dioxide  is  merely  made 
up  of  innumerable  numbers  of  these  smallest  quantities, 
and  so  the  percentage  composition  of  a  large  quantity  is 
exactly  the  same  as  of  the  very  smallest  quantity  that 
can  exist.  This  smallest  quantity  is  called  a  molecule. 
A  molecule  is  the  smallest  quantity  of  a  substance  that 
can  exist  in  the  free  state  or,  in  other  words,  that  can 
have  a  separate  existence. 

Dalton  considered  water  to  consist  of  one  atom  of 
hydrogen  and  one  atom  of  oxygen,  and  represented  it 
by  the  symbol  O  O-  Bnt  when  sodium  acts  on  water,  one- 
half  of  the  hydrogen  is  set  free,  and  one-half  of  it,  as  well 
as  all  of  the  oxygen,  combines  with  the  sodium.  The 
simplest  explanation  is  that  each  molecule  of  water  con- 
tains two  atoms  of  hydrogen  and  one  atom  of   oxygen. 


T 

ui 

Ci 

W 

th 


LAWS   OF  CHEMICAL    COMlilSATlON 


77 


a  Corn- 
ell was 
itrogen 
isented 
dt  that 
lioxide 

itity  of 
on  and 
>noxide 
i)stan(;e 
3xv<:jen 

I,'  o 

*ept  by 

of  oxy- 

e  ;  and 

IS   two 

lantity 

{  made 

ntities, 

itity  is 

y  that 

lecule. 

e  tliat 

t  can 

)m  of 
ted  it 
',  one- 
Is  well 
The 
n'  con- 
lygen. 


The  atom  of  oxygen  and  one  of  the  atoms  of  hydrogen 
unite  with  an  atom  of  sodium  to  form  a  moU'cule  of 
caustic  soda,  and  one  of  the  hydrogen  atoms  is  set  free. 
When  a  number  of  molecules  of  water  are  thus  broken  up, 
there  is  a  corresponding  amount  of  caustii'  so<la  produced 
and  a  quantity  of  hydrogen  gas.  I'here  is  no  metliod 
known  for  dividing  the  oxygen  in  water  into  two  parts, 
and  so  the  molecule  of  water  is  considered  to  contain  one 
atom  only  of  (►xygen.  In  liycb'ogi'ii  peroxide  there  is 
twice  as  much  oxygen  as  in  water,  and  the  oxygen  can 
be  divided  into  two  parts  ;  so  the  moh'culc  of  liydi'ogeu 
peroxide  is  considered  as  made  up  of  two  atoms  of  hydro- 
gen and  two  atoms  of  oxygen. 

The  atom  is  the  smallest  quantity  of  an  element  capable 
of  entering  into  chemical  reactions,  but  in  many  cases  there 
is  evidence  that  the  smallest  (juantity  of  the  element  that 
is  capable  of  a  separate  existence  consists  ot  tiro  atoms  and 
not  of  one.  l\\  such  a  case  the  nioh'cuh'.  of  the  element 
consists  of  two  atoms.  In  the  case  of  some  elements  the 
molecule  consists  t)f  more  than  two  atoms,  while  in  some 
cases  the  molecule  consists  of  only  one  atom.  Von  have 
not  arrived  at  the  stage  when  you  can  a[)preciate  all  the 
arguments,  but  you  have  Iciirned  one  fact  in  favour  of  the 
view  that  the  molecule  of  an  clement  may  contain  more 
than  one  atom. 

You  remendjcr  that  ozone  is  one  and  one-half  times  as 
heavy  as  oxygen.  If  there  are  the  same  numl)er  of  m(de- 
cules  of  ozone  in  a  given  space  as  there  are  of  oxygen  in 
the  same  s[)ace,  each  molecule  of  ozone  must  be  one  and 
one-half  times  as  lieavv  as  each  molecule  of  oxyofen.  But 
a  molecule  of  ozone  cannot  consist  of  an  atom  and  a  half, 
because  an  atom  cannot  be  divided  chemically;  we  can, 


^ 

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33  WIST  MAIN  STMIT 

WHSTM.N.Y.  14SM 

(716)  •73-4503 


4^ 


1^ 


78 


CHEMISTRY 


liowever,  conceive  that  the  molecule  of  oxygen  is  made 
up  of  two  atoms  of  the  element  and  the  molecule  of  ozone 
of  three  atoms.  As  most  of  the  common  elements  have 
two  atoms  in  tlie  molecule,  it  will  be  eusiest  to  learn  the 
exceptions  as  we  meet  them. 

The  Law  of  Gaseous  Volumes.  —  Shortly  after  Dalton's 
law  was  announced  and  his  atomic  theory  i)roposed,  Gay- 
Lussac,  a  French  chemist,  made  the  statement  frequently 
called  the  third  chemical  law,  or  The  Law  of  Gaseous 
Volumes.  The  law  states  tiiat  wlien  gases  combine  the 
volumes  of  tlie  gases  which  enter  into  combination  are 
very  simply  related  to  each  other  and  to  the  volume  of 
the  compound  produced,  when  the  latter  is  a  gas.  For 
instance,  two  volumes  of  hydrogen  unite  with  one  of 
oxygen  to  form  water;  and  if  the  temperature  is  high 
enough  so  that  the  water  is  in  the  form  of  vapour,  its 
volume  is  exactly  the  same  as  that  of  the  hydrogen. 
Three  volumes  of  hydrogen  and  one  of  nitrogen  are 
produced  from  two  volumes  of  ammonia.  Two  volumes 
of  carbon  monoxide  unite  with  one  volume  of  oxygen  to 
form  two  volumes  of  carbon  dioxide.  In  some  cases, 
though  in  none  that  we  have  dealt  with,  the  volume  of 
the  compound  is  extactly  equal  to  the  sum  of  the  volumes 
of  tl\e  constituents,  but  in  many  cases  there  is  contraction. 

Avogadro^s  Law.  —  Dalton's  law  stated  tliat  there  is  a 
simple  rehition  between  the  number  of  atoms  of  various 
gases  taking  part  in  chemical  reactions ;  Gay-Lussac's  law- 
stated  that  theie  is  a  simple  j'elatir>n  between  the  volumes 
of  the  gases ;  but  tlie  connection  between  the  two  laws 
did  not  make  itself  apparent  to  either  of  these  chemists. 
In  1811,  Avogadro,  an  Italian  i)hysicist,  tried  to  explain 
Gay-Lussac's  observation  by  an  hypothesis,  little  regarded 


LAWS  OF  C 11  EMU  A  L   COM  HI  NAT  ION 


'9 


is  made 
of  ozone 
nts  have 
earn  the 

Dalton's 

ed,  Gay- 

:;quently 

Gaseous 

bine  the 

tion  are 

dume  of 

IS.     For 

one   of 

is  high 

pour,  its 

drogen. 

gen   are 

volumes 

ygen  to 

cases, 

lume  of 

volumes 

raction. 

ere  is  a 

various 

ic's  law 

volumes 

\'o  laws 

lemists. 

explain 

Jgarded 


for  forty  or  fifty  years,  but  now  considered  of  the  greatest 
im[K)rtance.  The  statement  of  the  hypothesis  is  usually 
called  Avogadro's  Law. 

It  is  that  equal  volumes  of  gases  under  tlie  same  con- 
ditions of  temperature  and  pressure  contain  the  same 
nund)er  of  mojfcules.  We  really  made  this  assumption 
when  discussing  the  number  of  atoms  in  a  molecule  of 
oxygen  and  in  a  molecule  of  ozone,  because  we  assumed 
that  there  were  the  same  nund)er  of  molecules  of  ozone  in 
a  given  space  as  molecules  of  oxygen  in  the  same  space. 
Since,  as  is  well  known,  the  volume  of  gases  varies  with 
change  of  temperature  and  pressure,  it  is  evident  why 
similar  conditions  of  temperature  and  pressure  are  insisted 
on  in  Avogadro's  law.  In  (iay-Lussac's  law  the  same 
conditions  are  tacitly  assumed. 

If  Avogadro's  law  is  true,  it  is  evident  that  if  we 
know  the  relative  density  of  two  gases  we  shall  know  the 
relative  weights  of  their  molecules,  because  i\w  density  of 
a  gas  is  the  weight  in  unit  volume,  and  unit  volume  of  one 
gas  contains  just  as  many  molecules  as  unit  volume  of 
another  gas.  The  density  of  carbon  dioxide  is  to  that 
of  carbon  monoxide  as  11  :  7,  therefore  the  weights  of 
their  molecules  are  in  the  same  ratio. 

Avogadro's  law  makes  no  distincticm  between  element- 
ary gases  and  compound  gases.  The  weight  of  a  given 
volume  of  oxygen  is  abtren  times  that  of  the  sanu;  volume 
of  hydrogen,  and  so  the  weight  of  tlu;  molecule  of  oxygen 
is  sixteen  times  that  of  the  molecule  of  hydrogen.  'i1ie 
density  of  carbon  monoxide  \^  fourteen  times  that  of  hydro- 
gen, therefore  the  weight  of  tiie  molecule  of  carbon  mo- 
noxide is  fourteen  times  that  of  the  molecule  of  hydrogen. 
The  density  of  carbon  monoxide  is  exactly  the  same  as 


80 


CIIKMlsTliY 


i 


that  of  iiitrojTtMi  ;  tlicrcrore  the  wcii^Hit  of  the  molecules 
of  the  two  siil)stimces,  one  of  wliicli  is  an  element  and  the 
otliei'  a  cnin))oun(l,  is  exactly  the  same. 

There  has  been  a  <(r('at  deal  of  work  done  in  order  to 
determine  llie  relative  wei«,dit  of  the  atoms.  To  determine 
this  weight,  it  is  necessary  to  know  how  many  atoms  there 
are  in  the  mole(;ule  of  the  coniponnd  worked  with.  For 
instance,  when  Dalton  thon.q;ht  that  the  molecules  of  water 
consisted  of  one  atom  of  hydrojj^en  and  one  atom  of  oxygen, 
he  naturally  said  that  the  weight  of  the  oxygen  atom  was 
eight  times  that  of  the  hydrogen  atom,  because  he  knew 
that  the  Mcight  of  oxygen  in  water  is  eight  times  the 
weight  of  hydrogen.  Hut  now  when  we  think  that  the 
molecule  of  water  contsiins  two  atoms  of  hvdnxjfen  and  one 
atom  of  oxygen,  we  say  tliat  tlu^  atom  of  oxygen  weighs 
sixteen  times  as  nnich  as  the  atom  of  hydrogen,  because 
one  atom  of  oxvgen  wcijiflis  eiy^ht  times  as  much  as  two 
atoms  of  hydrogen. 

Ilvdrogen  is  the  li<djtest  substance  known,  and  its  atom 
is  often  taken  as  the  unit,  and  we  say  that  the  atomic 
weight  of  oxygen  is  10.  In  the  same  way  we  say  the 
atomic  weiglit  of  nitrogen  is  14,  of  carbon  12,  and  so  on 
for  all  the  elcnuMits. 

The  Present  Chemical  Symbols.  —  Dalton,  as  we  saw, 
used  synd)ols  for  the  atoms  of  dill'erent  elements,  but  his 
synd)ols  were  soon  replaced  by  the  first  letter  of  the  Latin 
name  of  the  element.  Very  often  the  Latin  and  the 
English  nanu's  corresixmd,  and  so  we  have  O  for  the  atom 
of  oxygen,  II  for  the  atom  of  hydrogen,  N  for  the  atom 
of  nitrogen,  ('  for  the  atom  of  carbon. 

The  nanu's  of  a  number  of  elements  begin  with  the 
sam«  letter,  and   in  this  ease  a  second  important  letter 


olecules 
and  the 

DFcler  to 
terniine 
lis  tlicre 
li.  Fur 
)f  water 
oxygen, 
Lorn  was 
le  knew 
ines  the 
that  the 
and  one 
[  weighs 
because 
as  two 

ts  atom 
atomic 

[say  the 
id  so  on 

e  saw, 
l)nt  his 
le  Latin 
nd  the 
lie  atom 
le  atom 

ith  the 
letter 


LAWS   OF  CHEMICAL    COMRIXAriOX 


81 


in  the  name  is  frequently  added  to  the  lirst  to  designate 
tlie  atom.  ('  stands  for  the  carbon  atom,  it  being  a  very 
important  element,  while  CI  stands  for  tlie  cidorine  atom, 
Cd  for  tlie  cadmium  atom,  and  (  s  for  the  ca'sium  atom. 
The  Latin  name  for  silver  is  ^in/rntuni,  and  tlie  symbol  for 
the  atom  is  A<s  the  Latin  name  for  H'nUl  is  ((Knini.  and 
the  symbol  for  the  atom  is  An. 

When  the  molecule  of  a  comi)onnd  is  to  be  re{)resented, 
the  synd)ols  of  the  atoms  are  put  together;  thus  (H) 
stands  for  the  molecule  of  carbon  monoxide.  If  there 
are  two  atoms  of  the  same  kind  in  the  m<>kH*ule,  the 
figure  is  written  at  the  right  hand  lower  corner  of  tin; 
symbol  for  the  atom;  thus  U._,()  U'[)resents  the  molecule 
of  water  containing  two  atoms  of  hydrogen  and  one 
atom  of  oxygen.  So  also  Nil;,  represents  a  molecule  of 
annnonia  containing  one  atom  of  nitrogen  and  three  atoms 
of  hydrogen. 

The  weight  of  the  molecule  is  got  at  by  adding  the 
weight  of  the  atoms  in  it  ;  the  weight  of  the  molecule  of 
ammonia  is  17,  because  the  weight  of  the  nitrogen  atom  is 
14,  and  that  of  the  three  hydrogen  atoms  JJ.  'I'lie  union 
of  sym])ols  to  represent  a  compound  is  usually  called  a 
formula.  As  has  been  said,  we  do  not  know  the  actual 
weight  of  atoms  or  molecules,  and  so  when  we  say  that  the 
weight  of  the  molecule  of  ammonia  is  17,  or  that  the 
molecular  weight  of  ammonia  is  17,  we  meiely  mean  that 
it  is  seventeen  times  the  weight  of  the  atom  of  hydrcjgen. 

Symbols  and  fornndie  always  should  nr.'an  a  certain 
definite  weight.  When  you  see  the  formula  N I  Ig,  it  should 
always  eonve}'  the  information  that  the  weight  of  the  nitro- 
gen is  to  the  weight  of  hydrogen  as  14  :  3.  It  is  a  conven- 
ient theory  that  a  large  quantity  of  ammonia  is  made  up 


82 


CHEMISTRY 


of  an  innumerable  number  of  molecules,  each  of  which  con- 
tains an  atom  of  nitrogen  and  tliree  atoms  of  hydrogen. 
There  are  mjiny  facts  wliich  make  this  theory  probable, 
and  no  facts  are  known  inconsistent  with  it,  but  it  is  only 
a  theory,  and  a  fact  to  which  the  theory  could  not  be 
reconciled  would  destroy  the  theory.  But  it  is  not  a 
theory  tliat  17  grammes  of  annnonia  contain  14  grammes 
of  nitrogen  and  3  grammes  of  hydrogen,  and,  therefore, 
that  84  grammes  of  ammonia  contain  28  grammes  of  nitro- 
gen .d  G  grammes  of  hy<lrogen,  so  the  formuhe  would 
remain  if  the  whole  atomic  theory  were  proved  incorrect. 
Hut  until  some  fact  is  discovered  to  upset  the  theory,  we 
may  consider  a  formula  as  representing  a  molecule  made 
up  of  atoms,  as  well  as  a  certain  definite  weight  made  up 
of  smaller  weights.  NII3  represents  a  molecule  or  seven- 
teen weights,  usually  (frammes^  of  ammonia.  But  the 
formula  NII3  should  not  be  used  in  general  instead  of 
the  name  ammonia. 


TAItLE  OF  ATOMIC  WEKillTS  OF  COMMON  ELEMENTS* 


Namk 

Symbol 

Atomic  Weight 

Aluminium  . 

. 

Al 

27.1 

Antimony     . 

• 

Sb 

120.0 

Argon  . 

•                 • 

A 

39.9? 

Arsenic 

• 

As 

75.0 

liariuin 

•                 • 

IJa 

137.43 

*  This  Uible  is  an  abstract  of  one  compiled  by  Kiclianls  in  1898.  The 
atomic  weight  of  oxygen  is  taken  as  16,  and  the  atomic  weights  of  the 
other  elements  are  compared  with  that.  If  hydrogen  as  unity  were 
made  the  standard,  the  numbers  representing  the  atomic  weight  would 
be  slightly  different. 


LAWS  OF  CHEMICAL   COM  HI  NATION 


8:i 


ich  con- 
Jrogen. 
I'obable, 
is  only 
not  be 
i  not  a 
ranimes 
ere  fore, 
>f  nitro- 
i  would 
correct, 
ory,  we 
le  made 
iiade  up 
I"  seven- 
kit  the 
tead  of 


lEXTS* 


Weight 


)? 

) 

V.\ 

!)8.  The 
ts  of  the 
ity  were 
It  would 


Namr 

Symbol 

Atomic  Wkicht 

IJismuth 

Bi 

208.0 

Boron    .... 

B 

10.95 

Bromine 

Br 

79.9 

Catlniiuni 

Cd 

112.3 

Calcium 

Ca 

•10.0 

Carbon 

C 

12.001 

ChloriiH' 

CI 

35.455 

Chromium    . 

Cr 

52.14 

Cobalt  .... 

Co 

59.00 

Copper. 

Cu 

03.(50 

Fluorine 

F 

19.05 

Gold     .... 

An 

197.3 

Hydrogen     . 

II 

1.0075 

Iodine  .... 

I 

12G.85 

Iron       .... 

F(i 

50.0 

Lead     .... 

Pb 

20(5.92 

Lithium 

Li 

7.03 

Magnesium  . 

Mg 

24.30 

Manganese   . 

Mn 

55.02 

Mercury 

"g 

200.0 

Nickel  . 

Ni 

58.70 

Nitrogen 

N 

14.045 

Oxygen  (Standard) 

() 

IG.OOO 

Phosphorus  . 

P 

31.0 

Platinum 

Pt 

195.2 

Potassium    . 

K 

39.140 

Selenium 

Se 

79.0 

Silicon  . 

Si 

28.4 

Silver    . 

Ag 

107.93 

Sodium 

Na 

23.050 

Strontium     . 

Sr 

87.08 

Sulphur 

S 

32.005 

Tellurium 

Te 

127.5 

Tin       .        .        . 

Sn 

119.0 

Zinc 

Zn 

05.40 

84 


riiEMismr 


i 


'i 


The  Kinetic  Theory  of  Gases.  —  C  losely  connected  with 
the  atomic  tlieory  is  tlie  "  Kinetic  Theory  of  (iases." 

It  is  considered  that  in  tlie  tliree  states  of  matter,  solid, 
liquid,  and  gaseous,  the  molecules  are  in  motion,  but  the 
motioit  is  different  in  ch.iracter  in  eacli  of  these  states. 

In  solids  the  molecules  move  tlirougli  a  limited  space 
with  a  somewliat  vibratory  nu»tion.  In  liquids  tliey  have 
a  mucli  wider  range,  but  are  always  under  the  influence 
of  other  molecules.  In  gases  the  motion  of  each  molecule 
is  almost  unaffected  by  the  other  molecules,  except  during 
collision.  The  motion  is,  therefore,  for  the  most  part  in 
straight  lines,  just  as  would  be  the  case  with  a  few  elastic 
balls  flying  about  in  a  room.  Such  balls  would  hit  jfgainst 
the  sides  of  the  room  and  rebound,  and  might  occasionally 
hit  each  other,  clianging  their  course  at  each  collision,  but 
for  the  most  part  moving  in  straight  lines.  In  gases  the 
space  between  the  particles  is  very  large  as  compared  with 
the  size  of  the  particles  themselves,  and  there  fee  gases  are 
easily  compressed.  The  pressure  of  gases  on  the  walls  of 
the  containing  vessel  is  due  to  impacts  of  the  particles, 
and  just  as  a  dozen  bails  flying  about  in  a  small  room 
would  hit  the  walls  more  often  than  the  same  number  of 
balls  in  a  large  room,  so  the  particles  of  a  gas  compressed 
into  a  small  volume  will  give  more  impacts  on  the  walls 
of  the  vessel,  and  therefore  exert  greater  pressure.  The 
higher  the  temperature,  the  more  rapidly  do  the  particles 
move,  and  therefore  the  greater  pressure  do  they  exert. 

Long  before  the  kinetic  theory  of  gases  was  proposed, 
it  had  been  discovered  that  gases  exert  a  greater  pressure 
when  confined  to  a  smaller  volume  and  when  raised  in 
temperature,  and  the  laws  governing  the  change  had  been 
investigated.  The  theory  explains  not  only  those  facts, 
but  many  others,  and  has  so  far  held  its  ground. 


ted  with 

(8." 

er,  solid, 

,  but  the 

atea. 

nd  space 

ley  have 

nfluence 

[nolccule 

t  during 

part  in 

*v  elastic 

t  {f  gainst 

isionallv 

jion,  but 

^ases  the 

fed  with 

ases  are 

walls  of 

articles, 

11  room 

mber  of 

pressed 

e  walls 

The 

articles 

fcert. 

Dposed, 

ressure 

ised  in 

d  been 

facts. 


CHAPTER    VIII 

COMMON   SALT  AND  SOME   SIMILAR  COMPOUNDS 

You  have  already  performed  some  experiments  with 
common  salt.  There  are  a  number  of  otlier  substances 
also  called  salts  because  they  are  in  maLy  respects  similar 
to  common  salt.  It  will  be  interesting  to  study  some  of 
them,  and  the  ones  chosen  are  among  tliose  most  similar 
to  common  salt,  and  are  selected  because  througli  them  we 
shall  be  led  to  the  consideration  of  some  substances  of 
very  great  chemical  interest  and  importance.  The  names 
of  tlie  salts  are  given  in  a  footnote*  so  that  tlie  ijacher  may 
see  at  a  glance  what  substances  to  provide,  but  the  names 
are  of  no  interest  to  us  just  now,  and  we  shall  designate 
the  salts  by  numbers.  We  shall  take  them  in  groups  of 
three,  numbering  them 

1  2  8 

I  5  i 

f  8  i 

the  first  on  the  list  being  common  salt. 

Experiments  with  Salts,  etc.  —  Experiment  33.  Taste 
a  number  of  the  substances,  taking  very  small  quantities. 
Several  of  them  are  medicinal,  though  common  salt  is  the 
only  one  used  with  ordinary  food.  You  have  already 
treated  common  salt  with  sulphuric  acid,  but  it  will  be 

*  The  salts  are  sodium,  potassium,  and  ammonium  clilorido,  bronudc, 
and  iodide. 

85 


8f') 


CHEMISTRY 


advjiiitajifeous  to  repeat  (he  experiment,  for  now  you  will 
l)e  able  to  conn)are  the  reaction  in  that  case  with  what 
takes  place  when  the  other  salts  are  treated  in  the  same  way. 

What  evidence  have  you  tiiat  a  gas  is  jiroduced  when 
sulphuric  acid  acts  on  No.  1?  What  are  tlie  properties 
of  the  gas?  See  if  you  can  discover  whether  it  is  heavier 
or  ligliter  than  air.  To  (?o  this,  hold  the  test-tube  in 
wliich  tlic  gas  is  produced  almost  horizontal,  and  see 
whether  tlie  fumes  rise  or  fall  as  they  come  from  the  tube. 
Draughts  blowing  through  the  laboratory  may  prevent 
the  success  of  your  experiment,  but,  if  so,  some  other  ob- 
servations later  on  should  decide  the  point.  What  about 
the  colour  and  odour  of  the  gas?  Does  it  burn?  Does 
it  support  the  combustion  of  a  match?  What  do  you 
observe  when  you  hold  a  drop  of  annnonia  water  on  a 
glass  rod  near  the  mouth  of  the  tube?  Under  what  cir- 
cumstances did  you  get  a  similar  result  before?  The 
substance  produced  is  the  same  in  both  cases.  What  is, 
therefore,  the  gas  coming  off  from  the  test-tube? 

Experiment  with  No.  2  in  the  same  way,  and  answer 
the  above  questions  in  so  far  as  they  are  applicable  to  it. 
Note  particularly  the  differences  between  the  action  in 
the  two  cases. 

Describe  the  action  of  No.  3  when  treated  in  the  same 
way. 

Now  see  which  of  the  other  salts  are  similar  to  No.  1, 
which  similar  to  No.  2,  and  which  similar  to  No.  3,  so  far 
as  the  action  of  sulphuric  acid  is  concerned. 

Experiment  34.  Mix  a  little  powdered,  manganese 
dioxide  with  No.  1,  and  again  treat  with  strong  sulphuric 
acid.  What  effect  has  the  manganese  dioxide?  How 
about  the  colour  and  smell  of  the  gas  ? 


W 


I 


' 


t 
a| 


roil  will 
th  what 
me  way. 
d  when 
operties 
heavier 
tube  ill 
111(1  see 
lie  tube, 
prevent 
ther  ob- 
it about 
!*  Does 
do  you 
er  on  a 
hat  cir- 
•^  Tlie 
Vhat  is, 

answer 
le  to  it. 
ion  in 

le  same 

No.  1, 
so  far 

ganese 
phuric 
How 


COMMOX   SALT  AND   HOMK  SIMILAR   f'OMPOrXDS      87 

Treat  a  little  of  No.  .3,  in  the  same  way,  with  manganese 
dioxide  and  sulphuric  acid.  What  evidence  have  you 
that  tlie  etfect  of  the  manganese  dioxide  is  not  so  great 
as  in  the  case  of  No.  1?  Now  try  the  same  experiment 
with  No.  2.  Arrange  the  salts  in  the  order  in  whitli  the 
addition  of  manganese  dioxide  is  effective,  beginning  with 
the  case  where  tlie  effect  is  greatest. 

You  should  now  have  an  idea  what  to  expect,  if  you 
treat  in  the  same  way  any  of  the  other  salts  ;  for  instance. 
No.  5  and  No.  9.  It  may  be  well  to  see  if  your  predic- 
tions are  veritied. 

Experiment  35.  Moisten  the  end  of  a  i)latinum  wire, 
dip  it  into  No.  1,  and  hoid  it  in  the  flame  of  a  lUmsen 
burner  or  of  an  alcohol  lamp.  What  is  the  colour  of  the 
flame?  Test  similarly  all  of  the  salts,  linding  out  which 
give  the  same  colour  as  No.  1.  While  doing  so,  make  a 
note  of  the  colour  of  the  different  flames.  Of  which  saUs 
is  the  flame  colour  most  persistent  ?  of  which  least  persist- 
ent ?     Which  substances  are  the  most  volatile  ? 

Under  what  circumstances  have  you  already  had  the 
same  coloured  flame  as  you  have  just  obtained  with  No.  1? 
In  the  former  experiments  hydrogen  was  produced  and 
was  burning.  What  reason  have  you  for  thinking  that 
the  colour  was  not  at  that  time  due  to  hydrogen?  If  the 
colour  was  not  produced  by  the  burning  of  the  hydrogen, 
what  must  have  given  it  ?  What  substance  do  you  now 
know  to  exist  in  common  salt  ?  What  other  salts  of  the 
set  contain  the  same  element  ?  Put  a  piece  of  glass,  such 
as  a  tube  or  rod,  into  the  flame.  What  is  one  of  the  con- 
stituents of  glass?  Watch  the  ordinary  non-luminous 
flame  and  notice  that  you  frequently  get  flashes  of  the 
same  colour,  due  to  dust  floating  about  the  laboratory. 


88 


CUKMlsriiY 


t 


m 


Y'ou  will  thus  set'  what  a  vury  Hinall  (juantity  of  this  par- 
ticuhvr  element  may  be  detected  l)y  the  colour  which  its 
compounds  give  to  the  flame.  The  great  Helgian  chemist, 
Stas,  succeeded  in  getting  a  flame  not  coloured  by  sodium, 
but  to  do  so  he  had  to  wet  the  walls  and  ceiling  and  floor 
of  the  room,  shut  it  up  for  three  days  so  that  the  dust 
might  settle,  and  he  even  then  allowed  no  one  to  enter  it 
but  himself.  What  metal  did  you  find  before  gives  the 
violet  flame  that  you  have  noticed  in  some  of  these  salts  ? 

Test  any  of  the  volatile  salts  by  mixing  it  with  a  little 
lime,  and  smelling.  What  information  have  you  obtained 
regarding  its  composition  ? 

Jn  what  respects  are  Nos.  1,  2,  and  3  alike?  In  what 
are  they  different  ? 

In  what  respects  are  Nos.  1,  4,  and  7  alike  ?  In  what 
are  they  different  ?  Compare  the  other  salts  in  the  same 
way.  Why  were  the  salts  arranged  in  three  groups  of 
three  ? 

Common  salt  is,  of  course,  the  most  important  as  well  as 
the  cheapest  of  all  these  salts,  and  we  shall  now  find  it 
advantageous  to  study  more  fully  the  compound  obtained 
by  the  action  of  strong  sulphuric  acid  upon  it,  though  as 
you  have  seen,  some  others  of  the  salts  examined  would 
give  off  the  same  gas  if  treated  in  the  same  way. 

We  shall  soon  be  able  to  find  out  what  else  there  is  in 
common  salt  besides  sodium,  and  soon  after  that  the  con- 
stituents of  the  other  salts. 


iliis  par- 
hicli  its 
chemist, 
sodium, 
ncl  floor 
he  cUist 
enter  it 
ives  the 
e  suits  ? 
I  a  little 
[)bt{iined 

III  what 

In  what 

;he  same 

oups  of 

well  as 

find  it 

)btained 

)ugh  as 

would 

jre  is  in 
the  con- 


CHAPTER   IX 


HYDROCHLORIC  ACID 


Preparation  of  Hydrochloric  Acid  and  Experiments  with 
the  Gas.  —  Expkkiment  36.  Fit  up  a  flask  as  in  Fig.  27. 
Into  the  flask  put 
a  handful  of  com- 
mon salt  and  cover 
it  with  sulphuric 
acid.*  Attach  a 
piece  of  rubber 
tubing  to  the  de- 
livery-tube so  that 
connection  may  be 
made  with  a  little 
glass  tower,  or  some 
other  vessel  con- 
taining lime.  You 
will  soon  be  able 
to  see  the  use  of 
the  lime.  It  is 
even  better  to  per- 
form   the    operation    under    a   hood.      Gently   heat   the 

*  The  strongest  sulphuric  acid  might  be  used,  but  it  is  liable  to  produce 

frothing,  and  a  better  strength  is  that  obtained  by  pouring  eleven  vobtmos 

of  strong  acid  into  eight  of  water.     The  solution  nnist  be  allowed  to  cool 

before  being  put  upon  the  salt.     Cold  acid  of  this  strength  does  not 

liberate  the  hydrochloric  acid  gas,  but  gentle  heating  is  sufficient  to  cause 

its  evolution. 

89 


o 


Fio.  27 


90 


CHEMISTRY 


I 


mixture  ot  2alt  and  acid  till  vou  see  effervescence  due 

i/ 

to  the  formation  "»f  gaseorj  hydrochloric  acid.  Heat 
carefully,  regulating  tne  temperature  according  to  the 
rapidity  with  which  you  desire  tlie  gas  to  come  off. 
After  tlie  gas  lias  come  off  long  e»iougli  to  drive  the  air 
out  of  the  flsi'^k,  disconnect  the  rubber  tubing  from  the 
tower  and  attach  to  a  glass  tube  having  a  jet.  Pass  the 
tube  tlirough  a  cork  wliich  can  fit  tiglitly  into  a  bottle 
and  push  it  down  t^U  it  reaches  the  bottom  of  the  bottle, 
placed  mouth  upward.  While  the  bottle  is  being  filled 
with  the  hydrochloric  acid  gas,  the  cork  must  be  only 
loosely  fitted  into  the  bottle.  Why  ?  How  can  you  tell 
when  the  bottle  is  full  of  gas  ?  When  it  is  full,  draw  out 
the  tube  that  passes  througii  the  cork  till  it  reaches  half- 
way to  the  bottom  of  the  bottle,  dis- 
connect the  rubber  tubing,  which  you 
should  at  once  attach  to  the  lime  tower, 
push  the  cork  tightly  into  the  bottle, 
turn  the  latter  upside  down,  putting 
the  end  of  the  tube  several  inches  be- 
neath the  surface  of  water  containing 
neutral  litmus  in  the  pneumatic  trough 
or  in  a  beaker.  It  may  be  well  to  sup- 
port the  bottle  in  the  ring  of  a  retort 
stand  as  shown  in  Fig.  28,  since  the 
experiment  may  take  several  minutes. 
Watch  the  Avater  inside  the  tube.  Why 
rise  ?  What  happens  when  it  reaches 
liie  top  of  the  tube?  What  have  you  learned  about  the 
solubility  of  hydrochloric  acid  gas  in  water?  What  is 
its  effect  on  litmus?  Why  would  it  be  inadvisable  to 
try  collect'' ng  hydrochloric  acid  over  water  ? 


Fio.  28 


does  U.  begin  to 


s 
s 

h 
h 

C 

a 
h 


HYDROCHLORIC  ACID 


91 


3nce  due 

i.      Heat 

y  to  the 

ome   off. 

e  the  air 

Prom  the 

Pass  the 

a  bottle 

le  bottle, 

ng  filled 

be  only 

you  tell 

draw  out 

lies  half- 

ttle,  dis- 

bich  3"ou 

le  tower, 

1  bottle, 

putting 

ches  be- 

ntaining 

c  trough 

to  sup- 

,  retort 

nee  the 

ninutes. 

.    Why 

reaches 

)Out  the 

yiiat  is 

able  to 


Experiment  37.  Arrange  an  apparatus  as  in  Fig.  29, 
connecting  the  rubber  tu'  ng  to  the  first  of  the  series  of 
bottles.  Pass  the  gas  for  some  time  through  the  bottles. 
What  evidence  have  you  during  the  operation  that  the 
gas  is  dissolved  by  the  water?  Aftei*  five  or  ten  minutes 
disconnect  and  taste  a  very  small  drop  of  the  liquid  in 
each  wash-bottle,  beginning  at  the  one  farthest  from  the 


Fig.  2<» 

generating  flask.  Which  bottle  contains  the  strongest 
solution  of  hydrochloric  acid  ?  Put  some  of  the  strongest 
solution  into  a  porcelain  evaporating  dish  and  heat  till  at 
least  three-quarters  of  the  liquid  is  evaporated.  Has  the 
hydrochloric  acid  all  gone  off  leaving  pure  water  behind  ? 
Compare  in  this  respect  the  evaporation  of  ammonia  water 
and  hydrochloric  acid  solution.  A  strong  solution  of 
hydrochloric  acid  is  made  commercially  by  absorbing  the 


1 


92 


CHEMIST  ar 


gas  in  water.  This  absorption  goes  on  in  very  large 
vessels,  and  the  gas  is  produced  in  very  large  furnaces 
holding  many  tons  of  salt  and  sulphuric  acid. 

Gently  pour  some  water  upon  the  top  of  a  concentrated 
solution  of  hydrochloric  acid.  A  good  way  to  do  is  to  half 
iill  a  test-tube  with  the  acid  and  to  incline  it  toward  the 
horizontal  till  the  acid  nearly  comes  out.  You  cjin  then 
easily  pour  water  on  the  top  of  the  acid  till  the  test- 
tube  is  three-quarters  full.  Does  the  water  lie  on  the 
top  of  the  acid,  or  does  it  sink  through  it  ?  By  using 
water  containing  litmus  the  position  of  the  water  may 
be  made  very  distinctly  visible.  Which  is  the  heavier, 
hydrochloric  acid  solution  or  pure  water  ?  How  does 
hydrochloric  acid  solution  compare  in  this  respect  with 
ammonia  water  ? 

KxPEUiMENT  38.  Collect  a  cylinder  of  the  gas  by 
downward  disi)lacement,  and  try  whether  a  lighted  candle 
or  taper  will  burn  in  it.  Also  try  the  same  experiment 
witli  burning  sulphur  and  phosphorus.  What  is  the 
result?  Would  you  call  hydrochloric  acid  a  supporter 
of  combustion  ?  Into  another  cylinder  of  tl^e  gas  plunge 
a  deflagrating  spoon  containing  burning  sodium.  What 
do  you  observe  ? 

KxTKitiMKNT  39.  Attach  the  rubber  tubing  to  a  tube 
simihir  to  that  which  you  used  in  Exp.  16,  but  instead  of 
hematite  put  mercuric  oxide  into  the  tube.  After  the  gas 
has  been  passing  a  few  minutes  without  heating,  what  do 
you  notice  in  tlie  end  of  the  tube  farthest  from  the  gen- 
erating fljisk  ?  What  two  substances  have  yor.  already 
found  to  exist  in  mercuric  oxide  ?  What  element  does  it 
sui)i)ly  in  order  to  produce  the  moisture  that  vou  see  cm 
the  glass  of  the  tube  ?     What  element  must  i^e  supplied 


JIYDROCHLORIC  ACID 


93 


ry  large 
furnaces 

entrated 
is  to  half 
^vard  the 
3an  then 
the  test- 
j  on  the 
\y  using 
,ter  may 
heavier, 
ow  does 
ect  witli 

gas  by 
(I  candle 
)eriment 
;  is  the 
ipporter 

plunge 
What 

b  a  tube 
itead  of 
the  gas 
hat  do 
lie  gen- 
|al  ready 
does  it 
see  c»n 
iipplied 


by  the  hydrochloric  acid?  What  is  one  of  the  elements 
composing  the  white  solid  produced  in  the  tube  ?  Does 
the  white  substance  consist  of  this  element  alone  ?  If  not, 
where  has  the  rest  of  it  come  from?  If  there  is  any  gas 
escaping  from  the  tube,  notice  its  coh)ur  and  smell  and 
test  it  with  litmus-paper. 

Experiment  40.  Fit  up  a  tube  similar  to  that  just 
used,  putting  in  small  pieces  of  manganese  dioxide  instead 
of  mercuric  oxide,  and  pass  hydrochloric  acid  gas  in  the 
same  way  as  before,  gently  heating  the  manganese  dioxide. 
How  far  is  the  result  similar  to  that  obtained  from  the  mer- 
curic oxide  ?  What  is  the  colour  of  the  gas  passing  out 
from  the  tube  ?  Does  it  smell  like  hydrochloric  acid  ? 
Smell  very  cautiously,  indeed.  What  is  its  action  on 
moistened  litmus-paper?  In  the  case  of  the  action  on 
mercuric  oxide,  what  became  of  that  part  of  tlie  hydro- 
chloric acid  that  is  not  hydrogen  ?  What  reason  have 
you  for  si.pposing  that  when  manganese  dioxide  is  acted 
on  by  hydrochloric  acid,  some  of  this  substance  escapes 
and  does  not  combine  with  the  manganese  ? 

Gases  obtained  by  Electrolysis  of  Hydrochloric  Acid 
Solution. — Experiment  41.  Electrolyse  a  strong  solu- 
tion of  hydrochloric  acid  in  the  same  way  as  you  electro- 
lysed water  in  Exp.  8,  or  you  may  use  a  more  elaborate 
apparatus  such  as  that  sliown  in  Fig.  ?}0.  The  electrodes 
should  be  of  gas  carbon,  since  chlorine  acts  on  platinum. 
Gas  carbon  is  a  hard  form  of  carbon  found  in  the  upper 
part  of  retorts  in  which  coal  is  distilled.  Test  the  colour- 
less gas  by  applying  to  it  a  lighted  match.  What  is  the 
gas?  What  is  the  colour  of  the  gas  in  the  other  tube? 
From  its  properties,  what  do  you  decide  regarding  the 
question  whether  you  have  already  met  this  gas  ?     If  you 


94 


CHEMISTRY 


are  told  that  the  quantity  of  water  in  the  electrolyte  is  just 
the  same  at  the  end  of  the  operation  as  at  tlie  beginning, 
from  what  must  this  gas  have  come  ?  On  account  of  its 
green  colour  it  is  called  chlorine,  from  the  Greek  word 
ehloros.     The  gas  now  called  chlorine  was  at  one  time 


Fi«.  30 


considered  a  compound  of  hydrochloric  acid  and  oxygen, 
and  was  called  oxy-muriatic  acid  (muriatic  acid  being  the 
earlier  name  for  hydrochloric  acid).  It  was,  however, 
found  impossible  to  get  oxygen  from  it,  and  as  chlorine 
has  never  been  decomposed  it  is  regarded  as  an  element. 
Hydrochloric  acid  is  a  compound  of  hydrogen  and  chlo- 


e  is  just 
ginning, 
it  of  its 
3k  word 
ne  time 


)xygen, 
;ing  the 
)wever, 
thlorine 
iiient. 
d  clilo- 


//  YDROCHL  on  If  A  (  ID 


05 


rine,  as  we  have  seen,  and  since  it  is  impossible  to  take 
away  part  of  the  hydrogen  from  hydrochloric  acid  with- 
out taking  it  all  away,  and  in  like  manner  it  is  imi)ossil)le 
to  take  away  part  of  the  chlorine  without  taking  it  all 
away,  the  molecule  of  hydrochloric  acid  is  considered  to 
consist  of  one  atom  of  hydrogen  and  one  atom  of  chlorine, 
and  is  represented  by  the  formula  IICI. 

Experiment  42.  Put  a  piece  of  sodium  (well  cleaned 
from  the  crust  which  usually  covers  it)  into  a  bulb  tube 
as  shown  in  Fig.  31 ;  connect  the  tube  with  the  generating 


Fia.  ai 

flask  and  fit  up  the  apparatus  in  such  a  manner  that  you 
can  collect  any  escaping  gas  in  a  test-tube  over  the  pneu- 
matic trough.  Let  a  current  of  hydrochloric  acid  pass  in 
the  cold  till  all  of  the  air  is  driven  out  of  the  apparatus. 
How  can  you  tell  when  this  is  the  case  ?  If  you  have 
been  collecting  the  air  in  the  test-tube,  fill  up  the  test-tube 
with  water  and  put  it  in  position  again.  Heat  the  sodium 
till  it  begins  to  burn,  then  remove  the  flame,  as  the  action 


96 


CUEMISTHY 


goes  on  of  itself.  When  the  burning  has  ceased,  continue 
to  pass  the  hydrochloric  acid  a  little  longer,  heating  tlie 
tube  where  the  sodium  was.  What  is  tiie  gas  collected 
in  the  test-tube  ?  Test  with  burning  matcli  or  splinter. 
Wliat  must  have  combined  with  the  sodium?  Wash  out 
the  substance  in  tlie  bulb  tube  with  a  little  water,  and 
evaporate  the  solution  till  quite  dry.  Moisten  with  a 
drop  or  two  of  water,  and  test  whether  it  is  acid,  alkaline, 
or  neutral.  It  should  be  neutral.  If  it  is  acid,  you  have 
not  dried  it  perfectly,  and  should  heat  it  again.  If  it  is 
alkaline,  add  a  drop  of  hydrochloric  acid  solution  till  it 
reddens  litmus-paper,  and  tlien  evaporate  off  the  acid. 
What  does  the  substance  taste  like  ?  What  is  the  compo- 
sition of  the  substance  ?  The  chemical  name  is  sodium 
chloride. 

Naming  of  Compounds  containing  Two  Elements.  —  We 
found  that  an  oxide  is  a  compound  of  oxygen  with  another 
element  (or  a  group  of  elements  that  acts  like  a  single 
element),  and  so  a  cliloride  is  a  compound  of  chlorin'^  and 
some  other  element  (or  group  of  elements  that  acts  like  a 
single  element). 

A  compound  of  two  elements  is  named  by  giving  the 
name  of  one  element,  while  the  name  of  the  other  ele- 
ment is  modified  so  as  to  end  in  the  syllable  -ide.  Zinc 
oxide  is  a  compound  of  tlie  two  elements  zinc  and  oxygen, 
magnesium  nitride  is  a  compound  of  the  two  elements 
magnesium  and  nitrogen,  and  sodium  chloride  is  a  com- 
pound of  the  two  elements  sodium  and  chlorine.  When 
one  of  the  elements  is  a  mei:al  and  the  other  is  not  a  metal 
(in  other  words,  is  a  non-metal),  it  is  the  latter  which  has 
the  ending  -ide.  Some  chemists  prefer  to  modify  the  name 
of  the  first  element  as  well,  changing  it  from  a  noun  to  an 


continue 
,ting  tlie 
collected 
si)liriter. 
^asli  out 
iter,  and 
1  with  a 
alkaline, 
you  have 
If  it  is 
on  till  it 
:he  acid, 
e  compo- 
s  sodium 

ts.  — We 

1  another 

a  single 

irin^  and 

!ts  like  a 

|ving  the 

her  ele- 

\e.     Zinc 

oxygen, 

elements 

a  com- 

When 

a  metal 

Ihich  has 

Ihe  name 

in  to  an 


IlYDnOCflLORIC  ACID 


97 


adjective,  and  to  say  sodic  chloride  instead  of  sodium  chlo- 
ride, and  thus  you  will  meet  both  forms  of  expression. 

Suppose  that  enough  hydrochloric  acid  had  not  been 
used  to  change  all  of  the  sodium  into  sodium  chloride, 
what  would  have  been  found  wlien  the  tube  containing  it 
was  washed  out?  What  reaction  would  it  have  to  litmus? 
Suppose  mor'j  hydrochloric  acid  used  than  necessary,  what 
reaction  would  the  solution  have  to  litmus?  Why  were 
you  told  to  continue  passing  the  hydrochloric  acid  gas 
after  the  sodium  had  ceased  to  burn  visibly  ? 

You  will  now  understand  what  was  meant  by  saying 
that  you  cannot  take  away  part  of  the  chlorine  from 
hydrochloric  acid  without  taking  away  the  whole.  It 
did  not  mean  tliat  if  you  have  a  large  (juantity  of  hydro- 
chloric acid  gas  and  a  small  piece  of  sodium,  that  the 
sodium  would  take  up  all  of  the  chlorine  from  the  hydro- 
chloric acid  ;  but  any  hydrochloric  acid  from  which  the 
whole  of  the  chlorine  has  not  been  taken  away,  has  been 
entirel}^  unaffected  and  might  as  well  not  have  been  pres- 
ent. The  sodium  took  all  of  the  chlorine  from  so  much 
of  the  hydrochloric  acid  as  it  acted  upon  and  set  free  all  of 
the  hydrogen.  This  is  different  from  the  action  of  sodium 
on  water ;  when  sodium  acts  on  water,  it  does  not  drive  out 
all  the  hydrogen  of  the  water  that  has  been  acted  upon, 
but  only  one-half  of  it ;  and,  as  we  saw,  we  consider  the 
proper  formula  of  the  molecule  of  water  to  be  Ilg^^  while 
we  consider  the  proper  formula  of  the  molecule  of  hydro- 
chloric acid  to  be  HCl.  In  the  same  way  we  consider 
the  formula  for  the  molecule  of  sodium  chloride  to  be 
NaCl. 

The  formula  for  the  molecule  of  water  is  HgO,  repre- 
senting that  two  atoms  of  hydrogen  are  united  to  one  atom 


98 


CHEMISTRY 


¥' 


of  oxygen.  liut  in  red  precipitate  we  assume  that  one  atom 
of  mercury  is  united  to  one  atom  of  oxygen,  and  in  lime, 
that  one  atom  of  cai'jium  is  united  to  one  atom  of  oxygen, 
hence  their  molecules  are  represented  by  the  formula) 
lIg(J  and  CaO.  VV^e  are  not  perfectly  {;ure  that  there  is 
only  one  atom  of  each  element  in  the  molecule,  but  we  do 
know  that  if  our  theory  of  atoms  is  correct,  there  are  as 
many  utoms  of  mercury  as  of  oxygen  in  mercuric  oxide, 
and  as  numy  atoms  of  calcium  as  of  oxygen  in  calcium 
oxide,  and  we  have  no  very  good  indication  that  there  is 
more  than  one  atom  of  each.  We  see  then  that  in  calcium 
oxide  one  atom  of  calcium  unites  with  one  of  oxygen, 
wliereas,  in  water,  ttvo  atoms  of  hydrogen  unite  with  one 
atom  of  oxygen.  One  atom  of  calcium,  therefore,  takes 
the  place  of,  or  is  equivalent  to,  two  atoms  of  hydrogen, 
and  tlie  equivalence  of  the  calcium  atom  is  two. 

Valency. —  We  usually  say  that  the  valence/  of  calcium 
is  two,  and  we  call  the  metal  a  bivalent  element.  One  atom 
of  cldorine  unites  with  one  atom  of  hydrogen,  and  we  say 
that  the  valency  of  cldorine  is  one,  or  that  it  is  a  univalent 
element.  One  atom  of  oxygen  unites  with  twc  atoms  of 
hydrogen,  and  so  oxygen  is  a  bivalent  element.  If  a 
bivalent  element  forms  a  compound  with  a  univalent 
element,  one  atom  of  the  former  requires  two  atoms  of  the 
latter.  If  two  bivalent  elements  unite,  they  can  unite 
atom  for  atom.  What  is  the  formula  of  the  molecule  of 
calcium  oxide  ?     What  of  calcium  chloride  ? 

Beginners  usually  have  difficulty  in  remembering  the 
valency  of  the  element,  and  so  do  not  know  how  many 
atoms  of  each  element  to  represent  as  existing  in  the 
molecule  of  the  compound.  Tlie  most  important  univa- 
lent metals  are  potassium,  sodium,  and  silver,  and  the 


;  one  atom 
[1  in  lime, 
f  oxygen, 
formula} 
t  there  is 
jut  we  do 
jre  are  as 
ric  oxide, 
I  calcium 
b  there  is 
n  calcium 
■  oxygen, 
with  one 
ore,  takes 
lydrogen, 

f  calcium 

One  atom 

id  we  say 

univalent 

atoms  of 

it.     If   a 

nivalent 

ns  of  the 

an  unite 

lecule  of 

ring  the 
>w  many 
in  the 


t 


univa- 
and  the 


HYDROCHLORIC  ACID 


99 


formulae  r^f  the  chlorides*  are  KCl,  NaCl,  and  AgCl.  It 
may  be  assumed,  in  the  meantime,  that  the  remaining  com- 
mon metals  are  bivalent.  Thus  we  have  ZnClj,  CaC'lg, 
PbClj,  MgClj,  and  the  corresponding  oxides,  ZnO,  CaO, 
PbO,  and  MgO. 

Tlie  metaly  that  have  other  valencies  will  be  learned  as 
you  proceed,  and  there  is  not  usually  much  trouble  with 
the  non-metals. 

You  have  had  the  opportunity  to  decide  whether  hydro- 
chloric acid  gas  is  heavier  or  ligliter  than  air,  but  if  you 
still  do  not  know,  you  should  before  going  on  try  some 
experiment  that  will  determine  the  point. 

Sodium  Sulphate  —  Double  Decomposition.  —  When  the 
hydrochloric  acid  is  all  driven  out  from  the  mixture  of 
salt  and  sulphuric  acid,  allow  the  flask  to  cool,  and 
dissolve  its  contents  in  water,  using  as  little  water  as 
possible,  so  that  you  may  liave  some  idea  as  to  the  solu- 
bility of  the  substance  (that  is,  whether  it  needs  much  or 
little  water  to  dissolve  it),  and  that  you  may  not  have 
very  much  water  to  evaporate  afterwards. 

Evaporate  the  solution  until  some  of  the  substance 
begins  to  crystallise,  and  allow  to  cool.  Are  these  crystals 
like  common  salt  in  their  taste  and  in  the  action  of  sul- 
phuric acid  on  them?  What  colour  do  they  give  to  the 
flame  when  tested  on  the  platinum  wire  ?  What  element 
is  there  in  these  crystals  which  exists  in  common  salt  ? 
What  part  of  the  sulphuric  acid  united  with  what  part  of 

*  The  full  statement  is  "  the  formula  of  the  molecule  of  the  chlorides," 
but  the  form  given  in  the  text  is  very  common.  It  should  never  be  for- 
gotten that  the  forumla  always  stands  for  a  certain  definite  amount  of  the 
substance,  and  shows  that  it  is  composed  of  the  elements  in  certain 
definite  proportiona. 


100 


CHEMISTRY 


tlie  common  salt  to  form  liydrocliloric  acid?  Sulphuric 
acid,  as  you  were  told  sonic  time  a<,^o.  contains  hydro- 
gen, suipliur,  and  oxygen,  and  •*  been  found  that 
the  formnla  IlgSO^  represents  the  molecule.  Usually 
when  one  element  is  removed  from  a  compound  another 
element  takes  its  place.  If  sodium  takes  the  i)lace  of 
hydrogen  in  sulphuric  acid,  it  might  be  expected  that  two 
bodies  could  be  formed,  one  whose  formula  would  be 
NallSO^,  and  another  whose  formula  would  be  NagSO^. 
These  two  substances  may  be  obtained  l)y  the  action  of 
suli)luiric  acid  on  common  salt,  and  one  of  the  arguments 
in  favour  of  the  foj'muhi  112^04  for  sulphuric  acid  is  that 
tliese  two  comi)ounds  can  be  made.  When  they  are  pro- 
duced by  the  action  of  sulphuric  acid  on  salt,  which  of 
them  will  be  obtained  in  a  given  case  dei)en(ls  upon  the 
relative  quantities  of  salt  and  sulphuric  acid  used  and  the 
temperature  to  which  the  mixture  is  heated,  the  higher 
temperature  giving  the  salt  with  the  greater  proportion 
of  sodium. 

Compounds  obtained  from  sulphuric  acid  by  replacing 
the  hydrogen  by  metals  are  called  sulphates.  Ordinary 
salt  is  formed  from  hydrochloric  acid  by  replacing  the 
hydrogen  of  hydrochloric  acid  by  sodium,  as  you  saw  in 
your  experiment  of  heating  sodium  in  a  current  of  the 
gtis.  Since  the  sodium  sulphates  are  produced  by  replac- 
ing the  hydrogen  of  sulphuric  acid  by  sodium  they  are 
also  called  salts.  When  the  sodium  of  common  salt 
replaces  the  hydrogcJi  of  sulphuric  acid,  tlie  hydrogen  at 
the  same  time  replaces  the  sodium,  uniting  with  chlorine 
to  form  hydrochloric  acid.  There  is  thus  "•  double  decom- 
position.'''  two  elements  or  groups  of  elements  changing 
places.     The  salt  derived  from  sulphuric  acid  by  replac- 


julpluiric 
s  liyd ro- 
und  that 
Usiuilly 
.  iiiiothcr 
place  of 
that  two 
t'oiikl  l)e 
NagSO^. 
ictiou  of 
fifiimeuts 
(I  is  that 
are  pro- 
^vhich  of 
ipou  the 
.  and  the 
p  higher 
oportion 

lephicing 
rdinary 
;ing  the 
saw  in 
of  the 
repUic- 
ley  are 
on  salt 
ogen  at 
;lilorine 
deeom- 
anging 
replac- 


IIYDROrULoniC  A('ll) 


101 


ing  half  of  the  liydrogLMi  by  sojliinn  is  sometinios  known 
as  sodium  hydrogen  siilpliate,  and  tiie  other  salt  disodiuni 
suli)hate.  Test  the  laboratory  specimens  of  tiiese  two 
salts  with  litmus.  Vou  should  lind  one  neutral  and  llie 
otlier  acid.  To  a  solution  of  tin;  acid  salt  ad<l  caustic 
soda  to  see  if  you  cannot  make  it  neutral.  Which  con- 
tains  the  most  sodimn,  tlic  acid  salt  or  the  neutral  salt  ?  Is 
the  sodium  hydrogen  suli)hate  the  acid  or  the  neutral  salt  ? 
Which  salt  has  a  formula  most  nearly  approaching  that  of 
sulphuric  acid?  The  names  acid  sodium  sul[»hate  and 
neutral  sodium  sul[)hate  are  more  frequently  used  than 
sodium  hydrogen  suli)hate  and  disodium  sulphate.  Even 
the  word  "neutral  "  is  often  left  out,  and  sodium  sul[)]iate 
means  the  neutral  salt.  Since  the  acid  suli)liate  rccjuires 
twice  as  much  acid  for  its  formation  as  the  neutral  salt 
does,  it  is  sometimes  called  the  bisuli)hate  ;  so  that  you 
see  there  are  occasionally  a  number  of  names  for  the  same 
substance,  each  name  laying  emphasis  on  a  different  fact. 
You  have  learned  that  sodium  chloride  acted  on  by 
sulphuric  acid  gives  h3^drochloric  acid  and  sodium  sul- 
phate or  sodium  acid  sulphate.  VV^hich  of  these  requires 
the  higher  temperature  for  its  })roduction  ?  The  way  in 
which  the  hydrogen  and  sodium  change  places  is  brought 
out  better,  if  we  cfill  sulphuric  acid  hydrogen  sulph.ate 
and  hydrochloric  acid  hydrogen  chloride,  as  the  formulae 
show  we  may  readily  do.  We  may  say,  sodium  chloride 
and  hydrogen  sulphate  yield  hydrogen  chloride  and  sodium 
sulphate.  If  at  tiie  i)roper  temperature  we, start  with  a 
certain  amount  of  sodium  chloride  and  add  just  the  right 
quantity  of  hydrogen  sul[)hate,  we  shall  obtain  all  of  the 
sodium  in  the  form  of  sulphate,  and  all  of  the  hydrogen 
in  the  form  of  chloride.     If  we  put  in  too  much  sulphuric 


102 


CHEMISTRY 


111 


acid,  we  shall  have  some  of  it  left  over;  if  too  little,  we 
shall  have  some  of  the  sodium  chloride  unchanged. 

Equations.  —  It  is  usual  for  (chemists  to  state  these  facts 
in  a  short  way  hy  using  *"  UqiKttlons.'"'  The  formula;  of 
the  substances  entering  into  the  reaction  are  written  first 
and  the  sign  -f-  is  put  between  them,  then  comes  the  sign 
of  equality,  and  then  the  products  of  the  reaction,  thus : 

NaCl  +  II2SO4  = /TC/ +  NaHSO^.* 

The  formula  NaCl  stands  for  a  certain  definite  amount 
of  sodium  chloride,  the  formula  HoSO^  stands  for  a  certain 
definite  amount  of  sulphuric  acid,  and  so  with  the  formula 
of  each  of  the  other  substances ;  and  hence  the  equation 
not  only  expresses  what  substances  are  produced  by  the 
reaction  of  the  other  substances,  but  also  how  much  of 
each  is  required  or  Produced  in  the  reaction.  'J'he  sym- 
bol Na  stands  for  23  parts  by  weight  of  sodium,  the 
symbol  CI  stands  for  35.5  parts  by  weight  of  chlorine. 
We  do  not  know  the  weight  of  the  atom  of  sodium  nor  of 
the  atom  of  chlorine,  but  we  know  that  the  atom  of  sodium 
weighs  23  times  as  much  as  the  atom  of  hydrogen,  and 
that  the  atom  of  chlorine  weighs  35.5  times  as  nnich  as 
the  atom  of  hydrogen.  In  a  molecule  of  common  salt, 
then,  the  weight  of  the  sodium  is  23  as  compared  with  the 
weight  of  chlorine  35.5,  and  if  we  assume  that  larger 
quantities  are  made  up  of  molecules,  for  every  23  ounces 
or  pounds  or  grammes  of  sodium  in  a  quantity  of  common 
salt,  there  must  be  35.5  ounces  or  pounds  or  grammes  of 
chlorine.     It  is  evident  that  the  quantity  of  common  salt 

*  In  the  equations  of  this  book  the  formulae  of  solids  are  printed  in 
black  type,  and  of  gases  in  italics.  Plain  type  indicates  that  the  substance 
is  a  liquid  or  in  solution. 


little,  we 
1. 

leHc  facts 
'inula;  of 
tt(Mi  first 
the  sign 
,  thus: 


amount 

a  certain 

I  formuhi 

equation 

d  by  tlie 

much  of 

riie  sym- 

ium,   tlie 

clilorine. 

in  nor  of 

f  sodium 

?en,  and 

nuch  as 

on  salt, 

ivith  the 

larger 

ounces 

onimon 

nmes  of 

ion  salt 

)rinted  in 
substance 


HYI)R(H'UU)lil(J  A(  ID 


10;] 


containing  this  quantity  of  sodium  and  chlorine  nuist  be 
58.5  ounces  or  pounds  or  grammes.  The  atom  of  sulj)hur 
weighs  32  times  as  much  as  the  atom  of  hydrogen,  and 
the  atom  of  oxygen  !♦>  times  as  much  as  the  atom  of 
hydrogen,  so  that  tlie  formula  IlgSO^  represents  tlie 
weight  2  -f  32  -h  (U  =  98,  and  t)ur  e(piation  represents 
that  98  parts  by  weight  of  sulphuric  acid  are  required 
for  58.5  parts  by  weight  of  common  salt.  Also  30.5 
grammes  of  hydrochloric  acid  would  be  i)ro(luced,  and 
120  grammes  of  sodium  acid  sulphate.  These  relationships 
of  weight  do  not  depend  upon  the  atomic  theory ;  they  are 
matters  of  experiment  and  have  to  deal  with  the  char- 
acter of  the  substances,  not  upon  any  theory  that  we  may 
liold  regarding  the  ultimate  structure  of  matter;  but  as 
during  nearly  a  hundred  years  the  atomic  theory  has 
stood  its  ground  and  no  facts  have  been  learned  to  upset 
it,  we  often  speak  as  tliough  we  were  as  sure  of  it  as  we 
are  of  the  experimental  results  obtained  by  analysis. 

It  must  be  remembered  that  equations  represent  only 
the  result  of  experiment ;  they  form  a  short  and  conven- 
ient method  of  describing  what  takes  place  in  a  reaction, 
but  what  does  take  place  can  be  learned  only  b}''  experi- 
ment. It  must  also  be  remembered  that  the  atomic 
weights  that  we  use  have  been  obtained  by  very  careful 
experiment.  Many  chemists  have  devoted  years  to  these 
experiments,  and  many  more  years  will  doubtless  be  ex- 
pended in  the  same  way  in  order  to  obtain  still  more 
accurate  results. 

You  bave  learned  enough  of  chemistry  by  this  time  to 
expect  that  the  weight  of  the  substances  produced  by  a 
reaction  must  always  be  equal  to  the  weight  of  the  sub- 
stances entering  into  the  reaction,  and  you  may  always 


104 


CHEMISTRY 


know  tliiit  an  equation  is  wrong  if  the  weight  represented 
on  one  wide  of  the  equation  is  not  exactly  equal  to  the 
weight  on  the  other  side,  or  (making  the  statement  in 
terms  of  atoms)  if  every  atom  represented  on  one  side  of 
the  equation  is  not  found  on  the  other  side  of  the  equa- 
tion. Jn  the  equation  Ave  have  heen  considering,  for 
example,  it  is  represented  that  one  atom  of  sodium,  one 
of  chlorine,  one  of  sulphur,  two  of  hydrogen,  and  four  of 
oxygen  (;nter  into  the  reaction.  Tliese  merely  change 
their  places,  and  in  tlie  products  there  are  one  atom  of 
sodium,  one  of  chlorine,  one  of  sulphur,  two  of  hydrogen, 
and  four  of  oxygen.  On  the  left  hand  side  the  two 
liydrogen  atoms  are  together  in  the  molecule  of  sulphuric 
acid ;  on  the  right  hand  side  they  are  separated  and  in 
different  molecules,  but  there  are  the  two  atoms  in  both 
cases. 

The  equation  does  not  tell  the  conditions  under  which 
the  exj)eriment  is  carried  out,  and  very  frequently  the 
course  of  the  reaction  depends  upon  the  conditions.  In 
this  case,  for  instance,  if  a  high  temperature  is  used,  the 
neutral  sodium  sulphate  is  produced,  and  the  equation  must 
represent  that  fact,  if  it  is  to  be  correct  for  these  conditions. 

The  equation  is 

2  NaCl  4- 1I2S(\  =  2  5"C;  +  NagSOi. 

The  2  in  front  of  the  formula  NaCl  means  that  two 
molecules  of  sodium  chloride  are  represented  as  entering 
into  the  reaction,  or  that  twice  the  quantity,  58.5  of 
sodium  chloride,  must  be  provided  for  98  of  sulphuric 
acid  to  act  upon.  It  will  be  seen,  then,  that  only  half  €as 
much  sulphuric  acid,  in  proportion,  is  needed  in  this  case 
as  in  the  former,  and  so  if  hydrochloric  acid  is  required,  it 


HYDROCHLORIC  ACID 


105 


3resented 
il  to  the 
ement  in 
le  side  of 
he  equii- 
riug,  for 
iiiiii,  one 
d  four  of 
'{  cliange 

atom  of 
ydrogen, 

tlie  two 
mlphuric 
I  and  in 
i  in  both 

3r  which 
ntly  the 
K)ns.  In 
sed,  the 
ion  must 
iditions. 


lat  two 
ntering 
58.5  of 
Iphuric 
half  as 
nis  case 
lired,  it 


would  appear  cheaper  to  use  a  liigh  temperature.  We 
must  always  consider  the  circunislances,  liowever,  before 
drawing  liasty  conclusions.  In  tliis  case  the  neutral  sodium 
sulphate  is  lia])le  to  harden  u[)()n  the  glass,  and  is  ditlicult 
to  remove  f'-om  the  llask,  wliilo  the  acid  sul[)hate  does  not 
present  this  dilHculty.  A  flask  broken  in  att(Mn[)ting  to 
clean  it  would  cost  more  than  the  extra  sul[)liuiic  acid. 
On  the  large  commercial  scale,  however,  it  is  cheaper  to  use 
a  high  temperature  and  a  smaller  quantity  of  sulpliuric 
acid,  and  besides,  in  the  conunercial  process  neutral  sodium 
sulphate  is  required  as  much  as  hydrochloric  acid  is. 

To  calculate  how  much  sul[)liuric  acid  is  reipiircd  to 
convert  a  given  amount  of  sodium  chloride  into  sulphate 
is  easy.  Suppose,  for  instance,  we  wish  to  know  how 
much  sulphnric  acid  is  required  for  100  grammes  of  sodium 
chloride.  We  kn  )W  that  for  2  x  58.')  =117  granunes  of 
sodium  chloride  98  grammes  of  sulphuric  acid  are  reqnired; 
therefore,  100  grammes  of  sodium  chloride  will  require 

98  X  };?  =  83.76  grammes. 

In  a  similar  way  it  could  be  calculated  how  much  hydro- 
chloric acid  and  how  much  sodium  sulphate  would  be 
})roduced. 

Statement  regarding  the  Occurrence  and  Properties  of 
Hydrochloric  Acid.  —  Hydrochloric  acid  is  to  a  certain 
extent  given  off  from  volcanoes,  or  from  the  lava  which 
has  recently  flowed  out  from  volcanoes,  but  the  amount 
is  comparatively  small.  The  method  of  its  prepM ration 
has  been  sul'liciently  discussed  and  so  have  most  of  its 
properties.  Its  density  c()m[)are(l  with  air  as  unity  is 
approximately  l.'iO.  At  the  temperature  of  10°  ( '.  it  liijue- 
fies  under  a  pressure  of  forty  atmospheres.     The  boiling 


106 


CHEMISTRY 


point  of  the  liquid  is  —  112.5°  C,  and  its  freezing  point 
is  —115°.  It  is  much  more  readily  condensed  than  such 
gases  as  oxygen  and  hydrogen,  and  was  one  of  the  first 
gases  to  be  compressed  into  the  liquid  form.  The  gas 
which  is  so  readily  condensed  is  also  readily  dissolved  in 
water,  and  at  0°  ( ■.  500  volumes  or  more  of  the  gas  are 
dissolved  by  one  volume  of  water.  The  strongest  solution 
has  a  specific  gravity  1.2.  When  the  strongest  hydro- 
chloric acid  solution  is  heated,  it  loses  a  greater  propor- 
tion of  gas  than  of  water,  ])ecoming  weaker  and  of  lower 
specific  gravity  until  it  readies  a  specific  gravity  1.1. 
On  the  other  hand,  when  a  very  dilute  solution  is  heated, 
more  water  in  proportion  is  given  off,  and  the  acid  becomes 
stronger  till  it  reaches  the  specific  gravity  1.1.  So  whether 
a  very  strong  or  a  very  weak  acid  be  evaporated,  the 
solution  ultimately  obtained  in  the  evaporating  vessel  will 
have  the  specific  gravity  1.1,  and  boil  at  the  temperature 
110°  C.  These  numbers  can  easily  be  remembered  and 
are  interesting.  Any  acid  either  stronger  or  weaker  boils 
at  a  lower  temperature  than  110°,  and  the  temperature 
will  be  the  lower,  the  stronger  the  acid,  if  its  specific 
gravity  is  more  than  1.1  ;  or  the  weaker  tlie  acid,  if  the 
specific  gravity  is  less  tlian  1.1.  If  there  were  just  a  very 
little  gas  dissolved,  the  boiling  point  of  tlie  solution  would 
be  very  near  to  100°,  tlie  boiling  point  of  pure  water. 
The  acid  of  1.1  specific  gravity  is  often  called  the  acid  of 
constant  boiling  point. 

Hydrochloric  acid  acts  on  zinc  and  iron,  setting  free 
hydrogen  in  just  the  same  way  as  sulphuric  acid  does,  the 
chloride  of  zinc  and  of  iron  being  produced  at  the  same 
time.  The  other  chemical  properties  of  hydrochloric  acid 
have  been  pretty  fully  studied  by  you  already. 


ng  point 
lan  such 
the  first 
The  gas 
olved  in 

gas  are 
solution 
:  hydro- 

propor- 
3f  lower 
ity  1.1. 
;  heated, 
becomes 
whether 
ted,  the 
ssel  will 
perature 
red  and 
ter  boils 
^erature 

specific 
1,  if  the 
t  a  very 

1  would 

water. 

acid  of 

ng  free 
oes,  the 
le  same 
'ic  acid 


CHAPTER   X 


THE  HALOGENS 


Laboratory  Preparation  of  Chlorine,  and  Experiments  with 
the  Gas.  —  Experiment  43.  Fit  up  an  apparatus  as  for 
making  hydrochloric  acid,  but  into  the  flask  put  about 
200  c.c.  strong  hydrochloric  acid,  and  then  about  one- 
quarter  of  its  weight  of  coarsely  powdered  manganese 
dioxide.  Heat  gently,  never  allowing  the  flask  to  become 
so  hot  tV  t  you  cannot  easily  hold  your  hand  on  it.  Why 
should  you  be  careful  not  to  heat  strongly  ?  When  strong 
hydrochloric  acid  solution  is  heated,  does  it  become  stronger 
or  weaker?     What  gas  is  produced  in  the  flask  ? 

A  hood  or  the  lime  tower  is  even  more  necessary 
in  these  experiments  than  in  the  preparation  of  hydro- 
chloric acid,  and  you  must  be  very  careful  not  to  inhale 
the  gas.  If  possible  the  operation  should  be  conducted 
under  a  hood.  Collect  a  number  of  bottles  or  cylinders 
of  chlorine  by  downward  displacement  or  over  hot  water. 
Does  hot  water  or  cold  absorb  gases  the  more  readily? 
Why  should  hot  water  be  used  when  chlorine  is  to  be 
collected,  while  hydrogen  is  usually  collected  over  cold 
water?  Strong  brine  would  serve  the  same  purpose  as 
hot  water. 

Is  chlorine  lighter  or  heavier  than  air?  Lower  a  small 
bottle  containing  air  into  a  larger  one  containing  chlorine, 
and  see  whether  you  can  dip  out  some  of  the  chlorine. 

Light  a  jet  of  hydrogen  and  introduce  it  into  a  jar  of 

i07 


108 


CHEMISTRY 


Fio.  32 


chlorine  as  in  Fig.  32.  What  change  do  you  notice  in  the 
appearance  of  the  hydrogen  flame?  What  change  in  the 
colour  of  the  gas  in  the  jar?     What  is  produced  when 

hydrogen  burns  in  chlorine? 

Light  a  candle,  and  liold  over  the 
flame,  just  above  the  luminous  part,  a 
test-tube  containing  cold  water  but  dry 
on  the  outside.  Wliat  do  you  now  see 
on  the  outside  of  the  test-tube?  What 
is  thus  shown  to  exist  in  the  candle? 
What  does  this  element  take  from  the 
air  in  order  to  produce  the  substance 
on  the  test-tube?  Would  anything 
else  have  appeared  on  the  test-tube  if 
held  in  the  luminous  part  of  the  flame  ? 
Now  introduce  the  lighted  candle  into  a  cylinder  of 
chlorine,  being  careful  to  lower  it  gradually.  What  proof 
have  you  that  there  is  a  part  of  the  candle  which  burns 
in  air  but  does  not  burn  in  chlorine?  What  part  of  the 
candle  does  burn  in  chlorine? 

Warm  a  little  turpentine  in  a  test-tube,  taking  care  that 
the  turpentine  does  not  catch  fire.  Dip  a  piece  of  filter- 
paper  into  the  turpentine  and  bring  it  at  once  into  a  jar 
of  chlorine.  If  your  experiment  is  successful,  the  tur- 
pentine will  catch  fire.  What  is  the  peculiarity  of  the 
smoke? 

What  two  elements  exist  in  ammonia?  WhicJi  of  them 
would  be  the  more  likely  to  ccmibine  with  chlorine?  What 
would  it  form?  What  would  be  produced  by  this  sub- 
stance combining  with  more  ammonia?  Put  a  piece  of 
paper  moistened  with  strong  ammonia  water  into  chlorine, 
and  see  if  your  results  are  what  you  might  expect.     Has 


THE  HALOGENS 


109 


ice  in  the 
ge  in  the 
lecl  when 

over  the 
us  part,  a 
)V  but  dry 
II  now  see 
3?  What 
}  candle? 
from  the 
substance 
anything 
st-tube  if 
lie  flame  ? 
iinder  of 
liat  proof 
ch  burns 
rt  of  the 

?are  that 
of  filter- 
ito  a  jar 
he  tur- 
of  tlie 

|of  them 

What 

[lis  sub- 

biece  of 

hlorine, 

Has 


the  substance  produced,  as  irritating  an  effect  on  the  eyes 
and  nose  and  throat  as  chlorine  has?  If  there  is  a  quan- 
tity of  chlorine  in  the  air  of  the  laboratory,  what  would 
be  a  convenient  substance  to  use  in  order  to  get  rid  of  it  ? 
Will  it  make  the  air  of  the  laboratory  look  more  or  less 
clear? 

Into  another  cylinder  of  chlorine  introduce  a  piece  of 
phosphorus  on  a  deflagrating  spoon.  Do  not  liglit  the 
phosphorus  before  putting  it  into  the  chlorine.  What 
evidence  have  3  ou  that  the 
chlorine  acts  on  the  phos- 
phorus? How  does  the 
behaviour  of  pliosphorus 
in  chlorine  compare  with 
that  of  phosphorus  in 
oxygen  ? 

As  in  Fig.  33,  shake 
some  finely  powdered  ar- 
senic and  finely  powdered 
antimony  into  the  chlorine 
contained  in  another  jar. 
What  do  you  observe  ? 
In  all  of  these  experi- 
ments be  specially  careful 
not  to  inhale  the  fumes, 
for  they  are  not  only  irri- 
tating but  very  poisonous. 

Heat  a  piece  of  sodium 
the  size  of  a  small  pea  or  less  in  a  deflagrating  spoon,  and 
so  soon  as  it  begins  to  burn,  introduce  it  into  chlorine, 
being  careful  that  none  of  the  sodium  sputters  into  your 
face.     Is  the  action  more  or  less  violent  than  when  burn- 


Fio.  SA 


110 


CHEMISTRY 


ing  sodium  is  introduced  into  liydrochloric  acid  gas  ? 
When  sodium  is  burning  in  hydrochloric  acid  it  must 
separate  the  chlorine  from  the  hydrogen.  Is  this  done 
when  sodium  is  burning  in  chlorine?  What  reason  is 
there  for  the  action  being  more  violent  in  one  case  than 
in  the  other  ?  What  substance  is  produced  when  chlorine 
acts  on  sodium  ? 

Chlorine  Water.  —  Bleaching.  —  Experiment  44.  Pass 
chlorine  into  water.  What  evidence  have  you  that  the 
water  absorbs  some  of  the  clilorine  ?  The  solution  of 
chlorine  is  usually  crlled  chlorine  ivater.  Pour  some  chlo- 
rine water  into  a  little  indigo  solution,  or  into  water  con- 
taining ink.  What  happens  to  the  colour?  Write  with 
ordinary  ink  on  a  piece  of  paper  on  which  there  is  print. 
What  difference  is  there  in  the  action  of  chlorine  water 
on  the  ink  with  which  you  have  written  and  on  the 
printer's  ink  ?  Put  a  piece  of  coloured  cloth  into  chlorine 
water  and  see  what  happens.  Chlorine  is  very  much  used 
for  bleaching  cloth,  paper,  and  numbers  of  other  things. 
It  is  not  usually  applied  in  the  form  of  chlorine  water, 
because  other  methods  are  more  convenient  on  the  large 
scale.  A  great  many  of  the  colouring  matters  are  sub- 
stances which  become  colourless  when  acted  on  by  oxy- 
gen ;  and  clilorine  with  water  produces  oxygen.  This 
may  be  shown  by  allowing  chlorine  water  to  stand  in  the 
sunlight  for  several  days,  when  the  greenish  colour  of 
the  water  disappears,  while  oxygen  and  hydrochloric  acid 
are  formed.     The  action  is  represented  by  the  equation 

2  HgO  -f  2  CI2  =  4  HCl  +  0^. 

If  some  substance  be  present  that  combines  readily  with 
oxygen,  the  chlorine  will  be  rapidly  used  up,  the  oxygen 


THE  HALOGENS 


111 


iid  gas  ? 
it  must 
his  done 
eason  is 
ase  than 
chlorine 

:4.    Pass 
that  tlie 
ution   of 
me  chlo- 
iter  con- 
rite  Avith 
is  print, 
ne  water 
on   the 
chlorine 
ich  used 
'  things. 
e  water, 
le  large 
lare  sub- 
by  oxy- 
This 
Id  in  the 
lour  of 
ric  acid 
tion 


ly  with 
oxygen 


not  being  set  free,  but  combining  with  the  other  sub- 
stance. The  reaction  will  not  require  several  days,  but 
in  all  probability  only  a  few  seconds.  The  colouring  mat- 
ters bleached  by  chlorine  are  usually  those  that  are  made 
colourless  by  oxygen.  Chlorine  and  water  and  the  colour- 
ing matter  produce  hydrocldoric  acid  and  a  colourless  sub- 
stance. Printer's  ink  is  composed  largely  of  lampblack, 
the  soot  from  burning  resin,  and  is  not  acted  on  by  oxy- 
gen, hence  is  not  bleached  by  chlorine  water. 

Chlorine  is  used  as  a  disinfecting  agent,  destroying 
noxious  odours  and  disease  germs.  The  action  is  some- 
what similar  to  that  in  bleaching ;  but  in  the  case  of 
disease  germs  chlorine  probably  acts  in  part  simply  by 
killing  those  lower  forms  of  life  in  the  same  way  as  it 
would  kill  higher  plants  and  animals.  Small  quantities 
of  chlorine  are  found  effective  for  the  purification  of 
drijiking  water,  any  excess  of  chlorine  being  removed  by 
filtering  through  charcoal. 

It  will  be  advisable  to  study  the  process  by  which  chlo- 
rine is  produced  from  manganese  dioxide,  and  to  express 
the  action  in  the  form  of  an  equation.  What  is  the 
formula  of  manganese  dioxide  ?  How  many  chlorine 
atoms  correspond  to  one  oxygen  atom ;  for  instance,  what 
is  the  formula  of  the  chloride  corresponding  to  the  oxide 
CaO  ?  What  is  the  ordinary  name  for  this  oxide?  What 
would  be  the  formula  of  the  chloride  corresponding  to 
manganese  dioxide  ?  This  chloride,  if  formed  at  all,  very 
readily  decomposes,  losing  half  of  its  chlorine,  which 
escapes  in  the  form  of  gas,  and  for  tliis  reason  chlorine 
can  be  obtained  by  the  method  described.  Why  cannot 
we  make  chlorine  by  the  action  of  hydrochloric  acid  on 
mercuric  oxide? 


112 


CHEMISTRY 


How  many  atoms  of  hydrogen  are  necessary  to  combine 
with  two  atoms  of  oxygen  ?  How  many  molecules  of 
hydrocJiloric  acid  are  necessary  to  supply  that  number 
of  hydrogen  atoms?  Putting  the  facts  you  have  learned 
into  the  form  of  an  equation,  we  have 

MnOo    4-    4HC1    =    MnCL    f   2  HJ)   4-    CU 


Manganese     Hydrochloric     Manganese 
dioxide  acid  chloride 


2 
Water 


2' 
Clilorine 


much 


;h 


d 


free 


dorine  in  hydrochloric  s 
as  gas  ?  What  becomes  of  the  rest  of  it  ?  The  equation 
represents  that  4  x  36.5=146  grammes  of  hydrochloric 
acid  are  required  for  87  grammes  of  manganese  dioxide. 
Why  should  the  acid  that  you  took  weigli  at  least  four  or 
five  times  as  much  as  the  manganese  dioxide,  if  you  desired 
to  use  up  all  of  the  manganese  dioxide?  Would  36.5 
grammes  of  the  acid  you  took  be  represented  by  the 
formula  HCl? 

Number  of  Atoms  in  the  Molecule  of  Hydrogen  and  of 
Chlorine.  —  In  our  equations  we  usually  wish  to  represent 
molecules  as  taking  part  in  the  reaction.  How  many 
atoms  are  there  in  a  molecule  of  hydrogen  ?  How  many 
in  a  molecule  of  chlorine  ?  In  order  to  represent  the 
reaction  which  takes  place  when  hydrogen  burns  in  chlo- 
rine, which  is  the  better  form  of  equation. 


or 


H  +  CI  =  HCl, 
H^+  Cl^=2HCU 


It  is  found  by  experiment  that  one  volume  each  of  hydro- 
gen and  chlorine  unite  to  form  two  volumes  of  hydrochloric 
acid.  If  Avogadro's  law  is  true,  that  equal  volumes  of  dif- 
ferent gases  contain  the  same  number  of  molecules,  could 


cl 

cl 

hi 

w 


THE  HALOGENS 


113 


combine 

scules   of 

number 

B  learned 


hlorine 


s  set  free 
equation 
rochloric 
dioxide, 
it  four  or 
u  desired 
.uld  36.5 
L   by  the 

• 

n  and  of 

epresent 
\v  many 

w  many 
Isent  the 

in  chlo- 


hydro- 
[ochloric 
}s  of  dif- 

,  coukl 


H  represent  the  molecule  of  hydrogen,  and  CI  the  mole- 
cule of  chlorine,  HCl  representing  the  molecule  of  hydro- 
chloric acid  ?  On  this  last  assumption  what  volume  of 
hydrogen  would  be  represented  by  H,  what  volume  by  CI, 
what  volume  by  HCl  ? 
What  would  the  equation 

jy-h  01  =  HCl 

represent  in  that  case  regarding  the  volumes  of  hydrogen, 
chlorine,  and  hydrochloric  acid  ?  Would  that  represent 
the  facts  of  experiment  ? 

What  is  the  weight  of  chlorine  as  compared  with  hydro- 
gen ?  If  we  use  the  symbol  H  to  represent  a  gramme  of 
liydrogen,  what  weight  would  be  represented  by  Hj? 
What  weight  by  C\^  ? 

Does  a  gas  expand  or  contract  if  more  pressure  is  put 
upon  it  ?  Does  it  expand  or  contract  if  its  temperature  is 
raised?  Two  grammes  of  hydrogen  always  occupy  the 
same  volume  if  the  temperature  and  pressure  are  the 
same.  It  is  usual  to  give  the  volume  of  a  gas  at  the  tem- 
perature of  melting  ice,  0°  C,  and  the  ordinary  atmospheric 
pressure,  which  is  the  pressure  that  would  be  exerted  by  a 
column  of  mercury  760  millimetres  high.  Two  grammes 
of  hydrogen  represented  by  the  formula  Hg  at  the  tem- 
perature 0°  C.  and  the  pressure  760  millimetres  occupies 
the  volume  22.253  litres.  Also  71  grammes  of  chlorine 
represented  by  the  formula  Clg  occupies  the  volume  22.253 
litres  at  0°  C.  and  760  millimetres.  This  volume  is  called 
the  gramme  molecular  volume,  because  it  is  the  volume 
which  the  gas  occupies  if  the  symbols  which  represent  the 
molecular  weight  are  used  to  represent  grammes.  Hydro- 
chloric acid  is  a  gas  whose  molecular  weight  is  represented 


114 


CHEMI8TRY 


by  the  formula  HCl,  and  the  weight  30.5  grammes  occu- 
pies tlie  volume   22.253  litres.     What  volume  is  repre- 
sented by  the  formula  2  HCl  ? 
What  does  the  equation 

^^+(7/2=2  HCl 

represent  regarding  the  volumes  of  the  gases  ? 

When  water  vapour  is  formed  from  hydrogen  and  oxy- 
gen, the  equation  representing  the  reaction  is 

H^+0  ==H^0, 
or  2  R^+  0,^=^2  H^O. 

Which  is  the  better  form  of  equation  ?  Which  represents 
the  molecule  of  oxygen  ?  What  volume  of  water  vapour  is 
obtained  from  two  volumes  of  hydrogen  united  to  one 
volume  of  oxygen  ? 

Ideas  criveyed  by  a  Chemical  Formula.  —  A  chemical 
formula  should  always  repi'esent  «^ne  of  three  things  : 

First,  a  molecule  of  the  substance  as  made  up  of  a  num- 
ber of  atoms,  each  having  a  certain  definite  weight  which 
we  do  not  know,  though  we  know  with  a  fair  degree  of 
accuracy  the  weight  of  one  atom  as  compared  with  that 
of  another.  The  molecular  weight  is  the  weight  as  com- 
pared with  that  of  an  atom  of  hydrogen. 

Second,  a  weight  of  the  substance  in  grammes,  one 
gramme  being  made  the  unit  of  weight  instead  of  the 
unknown  weight  of  the  atom  of  hydrogen.  The  formula 
then  represents  the  gramme  molecule. 

Third,  in  the  case  of  gases  and  of  gases  only,  a  certain 
definite  volume  called  the  gramme  molecular  volume,  which 
is  the  volume  of  the  gramme  molecule  of  the  gas  at  0°  C. 
and  760  millimetres  pressure.    There  is  no  simple  relation 


THE  II A  LOG  EX  S 


115 


nes  occu- 
is  repre- 


and  oxy- 


represents 

vapour  is 

}cl  to  one 

chemical 
things  : 
tf  a  num- 
;ht  which 
ilegree  of 
^vith  that 
It  as  coni- 

imes,  one 
Id  of  the 
formuhx 

la  certain 

pe,  which 
at  0°  C. 
relation 


between  the  volume  and  the  weiglit  of  liquids  and  of  solids, 
as  there  is  of  gases,  and  hence  formuhe  do  not  represent 
volume  in  these  cases.  We  can  tell  from  the  formula  of 
hydrochloric  acid  what  the  volume  of  a  certain  weight  of 
the  gas  would  be  at  0°  C.  and  700  millimetres  pressure, 
hut  we  cannot  tell  from  the  formula  what  the  volume  of 
water  or  sand  would  be  under  tlie  same  conditions.  Know- 
ing that  tlie  formula  of  the  molecule  of  oxygen  is  O^',  how 
many  grammes  of  oxygen  occupy  the  volume  22.253  litres? 
How  many  grammes  of  nitrogen  occupy  the  same  volume? 
Air  is  made  up  of  these  two  elements  for  the  most  part, 
and  the  weight  of  air  occupying  the  volume  22.253  litres 
is  28.88  grammes.  If  we  know  the  molecular  weight  of  a 
gas,  we  can  therefore  always  tell  whether  it  is  lighter  or 
heavier  than  air. 

Bromine.  —  What  is  obtained  when  strong  sulphuric 
acid  acts  on  common  salt  ?  What  is  obtained  when 
hydrochloric  acid  acts  on  manganese  dioxide  ?  You  re- 
member that  you  treated  No.  1  of  the  series  of  salts  in  the 
last  chapter,  with  manganese  dioxide  and  sulphuric  acid. 
What  was  the  gas  obtained  in  tliat  case  ?  What  was  the 
appearance  of  the  vapour  obtained  from  No.  2  by  the  same 
action  ?  Was  the  metal  in  No.  2  the  same  as  in  No.  1,  or 
was  it  different  ?  What  reason  have  you  for  supposing 
that  the  vapour  obtained  by  the  action  of  manganese 
dioxide  and  sulphuric  acid  was  similar  to,  though  not 
identical  with,  chlorine  ?  The  vapour  was  that  of  bromine, 
so  named  on  account  of  its  very  disagreeable  and  irritat- 
ing odour  (from  the  Greek  word  hromos). 

What  is  the  chemical  name  of  No.  1,  which  you  found 
to  consist  of  sodium  and  chlorine  ?  What  is  the  name  of 
No.  2,  which  you  now  know  to  consist  of  sodium  and 


116 


CUEMISTUY 


bromine  ?  What  is  obtained  by  the  action  of  sulphuric 
acid  on  sodium  chh)ride  ?  Wliat  might  you  expect  to  get 
by  the  action  of  sulphuric  acid  on  sodium  bromide  ? 
What  evidence  have  you  that  if  hydrobromic  acid  is 
obtained  at  all  it  is  not  the  only  thing  obtained?  What 
elements  do  you  judge  from  the  name  hydrobromic  acid 
to  exist  in  that  substance?  What  reason  have  you  for 
supposing  that  they  do  not  form  so  Htahle  a  compound 
(that  is,  a  compound  difficult  to  decompose)  as  hydrogen 
and  chlorine?     VV^ould  you  expect  hydrogen  to  burn  in 

bromine  as  readily  as  in 
chlorine  ? 

Exi'EitiMENT  45.  Try 
whether  a  jet  of  hydrogen 
will  burn  in  bromine  va- 
pour. To  do  this  put  a 
few  drops  of  liquid  bro- 
mine into  a  wide-mouthed 
bottle,  or  into  a  flask 
shapecl  like  that  in  the 
figure  (Fig.  34).  Such 
a  flask  is  called  an  Erlen- 
meyer  flask,  and  may  be 
warmed  without  danger 
of  breaking.  Introduce 
a  burning  jet  of  hydrogen. 
What  is  the  result  ?  If 
you  have  no  liquid  bro- 
mine at  hand,  you  can 
prepare  some  of  the  vapour  from  potassium  bromide. 
Slowly  add  eleven  volumes  of  strong  sulphuric  acid  to 
eight  volumes  of  water,  and  when  the  mixture  is  cool  mix 


Fia.  34 


THE  irALOGH.ys 


117 


ulphuric 
ct  to  get 
iromide  ? 

jicid  is 
!  What 
niic  acid 

you  for 
jiiil)OUiid 
lydrogeu 

burn  in 
ily  as  in 

45.    Try 

lydrogen 

mine  va- 

lis  put  a 

uid  bro- 

moutlied 

a    flask 

t  in  the 

Such 

n  Erlen- 

may  be 

danger 

itroduce 

drogen. 

lit  ?     If 

id  bro- 

rou   can 

tromide. 

acid  to 

;ool  mix 


with  manganese  dioxide.  This  may  be  (h>ne  in  tlie  Krlen- 
meyer  Ihisk.  'I'iien  a(hl  potassium  bromide  as  required, 
and  heat  gently.  Introduce  a  candle  int(>  the  bromine 
vapour.  Does  it  burn?  If  you  have  licpiid  bromine 
pour  a  few  drops  of  it  into  turi)entine.  If  not,  pour 
some  of  the  bromine  vapour  into  turpentiiu'  and  shake 
up  so  that  the  bromine  may  come  into  contact  witli 
the  turpentine.  What  evidence  liave  you  that  chemical 
action  lias  taken  place  ?  What  evidence  have  you  that 
the  action  is  not  so  violent  as  when  chlorine  acts  on  tur- 
pentine? Turpentine  consists  of  carbon  and  hydrogen; 
when  chlorine  acts  on  it,  the  hydrogen  is  all  removed  and 
the  carbon  set  free  as  a  dense  smohe.  When  bromine  acts 
on  it,  a  part  only  of  the  hydrogen  is  removed,  and  some 
bromine  takes  its  place,  giving  a  colourless  comj)ound. 
This  process  is  called  suhstlfution.  We  say  that  bromine 
is  substituted  for  part  of  the  hydrogen,  or  that  part  of  the 
hydrogen  is  replaced  by  bromine.  The  hydrogen  removed 
combines  with  bromine,  forming  colourless  hydrobromic 
acid.  Half  of  the  bromine  that  enters  into  the  reaction 
replaces  hydrogen,  the  other  lialf  combines  with  the 
hydrogen  so  replaced. 

Experiment  46.  Introduce  into  bromine  vapour  a 
piece  of  phosphorus  in  a  deflagrating  spoon,  as  in  Fig.  35. 
What  do  you  observe  ?  Set  fire  to  a  piece  of  sodium,  and 
put  it  into  bromine  vapour.     What  is  produced  ? 

ExPEKiMENT  47.  Put  a  few  drops  of  bromine  into  about 
ten  times  as  much  water.  What  evidence  have  you  that 
water  dissolves  bromine  ?  Does  bromine  mix  with  water 
in  all  proportions  as  alcohol  does  ?  Which  is  the  heavier 
of  the  two  liquids  ?  Add  a  few  drops  of  bromine  water 
to  a  larger  quantity  of  water,  and  then  add  a  little  carbon 


•ts^,^ 


118 


CHEMISTRY 


bisulphide  (or  disulphide).*  What  elements  do  you  judge 
by  the  name,  to  exist  in  carbon  bisulphide  ?  Remember- 
ing the  formula 
of  carbon  diox- 
ide, what  would 
you  expect  the 
formula  of  car- 
bon disulphide 
to  be  ?  Is  car- 
bon  bisul- 
phide heavier  or 
lighter  than 
water  ?  Does  it 
dissolve  bro- 
mine more  or 
less  readily  than 
water  ?  What 
is  the  colour  of 
a  solution  of 
bromine  in  car- 
bon bisulphide? 
To  some  water  containing  a  little  ink,  or  similar  colour- 
ing matter,  add  bromine  water  slowly  until  you  see  some 
decided  effect.     What  is  the  effect  ? 

To  a  solution  of  potassium  bromide  add  a  few  drops  of 
chlorine  water,  and  then  a  little  carbon  bisulphide.  What 
Ir.  the  colour  of  the  carbon  bisulphide,  when  the  liquid  is 
shaken  up  ?  To  what  is  the  colour  due  ?  If  just  enough 
chlorine  water  were  added,  and  the  bromine   produced 


Fio.  35 


*  The  name  disulphide  is  not  so  f^od  as  bisulphide,  for  the  prefix  is 
Greek  and  the  main  part  of  the  word  is  Latin. 


THE  HALOGENS 


119 


Oil  judge 
member- 
formula 
on  diox- 
at  would 
pect  the 
I  of  car- 
sulphide 
Is  car- 
fa  i  s  u  1  - 
eavier  or 
e  r    than 
Does  it 
ve   bro- 
more    or 
dily  than 
What 
colour  of 
tion     of 
in  car- 
Iphide  ? 
colour- 
ee  some 

[drops  of 
What 
liquid  is 
enough 
Iroduced 

prefix  is 


were  removed,  wliat  substance  would  be  left  in  solution 
in  the  water? 

Since,  when  chlorine  is  added  to  a  metallic  bromide, 
bromine  is  set  free,  chlorine  is  said  to  have  a  stronger 
affinity  for  a  metal  than  bromine  has.  Did  sodium  burn 
more  or  less  violently  in  bromine  than  in  chlorine  ? 

Iodine.  —  What  happened  when  you  treated  No.  3  of 
the  series  of  salts  with  manganese  dioxide  and  sulphuric 
acid  ?  Was  the  substance  obtained  either  chlorine  or 
bromine  ? 

Experiment  48.  Repeat  the  experiment,  gently  heat- 
ing the  lower  part  of  the  test-tube.  Notice  what  collects 
in  the  upper  part  of  the  tube.  Is  it  a  solid  or  a  liquid  ? 
What  is  its  colour?  What  is  the  colour  of  the  vapour  before 
condensation  ?  The  substance  is  called  iodine  on  account 
of  this  colour,  the  name  being  derived  from  a  Greek  word, 
as  are  most  of  the  names  in  chemistry.  What  is  the 
chemical  name  of  No.  3  ? 

Experiment  49.  Add  some  iodine  to  turpentine. 
What  evidence  have  you  that  it  acts  less  energetically 
than  bromine?  What  action  is  there ?  Put  a  small  piece 
of  phosphorus  in  a  bottle  or  on  a  block  of  wood,  and 
sprinkle  a  little  iodine  upon  it.  You  should  find  that 
the  union  producf^s  flame,  so  you  must  be  careful. 

Experiment  50.  Try  to  dissolve  iodine  in  water.  Is 
it  readily  or  sparingly  soluble  ?  What  is  the  colour  of  the 
solution?  Now  add  a  little  carbon  bisulphide  to  the 
aqueous  solution  (the  solution  in  water).  Does  iodine 
dissolve  better  in  water,  or  in  carbon  bisulphide  ?  To 
a  solution  containing  a  very  little  potassium  iodide  (a 
very  small  crystal  in  a  good  deal  of  water),  add  a  few 
drops  of  bromine  water  and  a  little  carbon  bisulphide,  and 


120 


CHEMISTRY 


tlien  shake.  Does  the  carbon  bisulphide  assume  the  col- 
our due  to  bromine  or  to  iodine?  Which  of  these  ele- 
ments has  the  greater  affinity  for  potassium  ? 

ExPEiiiMEXT  51.  Grind  up  a  few  grains  of  starch  with 
enough  cold  water  to  make  a  fluid  of  a  creamy  consistence, 
then  add  to  about  twenty  times  as  mucli  boiling  water, 
and  boil  half  a  minute  or  so.  Dissolve  a  very  little  potas- 
sium iodide  in  water  and  add  a  few  drops  of  the  starch 
paste  just  made.  What  is  the  colour  ?  Then  add  a  drop 
or  two  of  chlorine  water.  What  change  is  there  in  the 
appearance  of  the  starch  ?  Divide  the  liquid  into  two 
parts.  Heat  one.  What  happens  to  the  colour  ?  Allow 
to  cool  and  notice  the  colour  again.  To  the  second  por- 
tion add  a  little  caustic  potash  or  soda.  Wliat  about  the 
colour?  What  is  the  effect  of  allowing  to  stand  in  this 
case  ? 

Statement  regarding  the  Occurrence,  Preparation,  and 
Properties  of  Chlorine,  Bromine,  and  Iodine.  —  You  have 
now  learned  a  good  deal  about  chlorine,  bromine,  and 
iodine.  You  naturally  do  not  expect  them  to  be  found 
free  in  nature  because  they  so  readily  act  on  other  sub- 
stances. Sea-water,  as  every  one  knows,  contains  common 
salt  more  than  half  of  whose  weight  is  chlorine.  It  also 
contains  bromides,  but  the  bromine  is  less  than  ^^^  part 
of  the  chlorine.  It  also  contains  iodides,  but  in  exceed- 
ingly small  quantity. 

When  a  salt  crystallises  from  a  solution  the  liquid  left 
behind  is  called  the  mother  liquor.  The  mother  liquor  ob- 
tained from  sea-water  by  evaporating  till  tl  common 
salt  has  separated  out  has  a  bitter  taste  on  account  of 
the  magnesium  salts  in  it,  and  is  called  bittern.  It  con- 
tains most  of  the  bromine,  which  can  be  extracted  either 


THE  HALOGENS 


121 


e  the  col- 
these  ele- 

arch  with 
iisistence, 
ng  water, 
tie  potas- 
he  starch 
1(1  a  drop 
J  re  ill  the 
into  two 
?  Allow 
cond  por- 
[iboiit  the 
id  in  this 

tion,  and 

'(HI  Iiave 
line,  and 
|be  found 
her  sub- 
common 
It  also 

exceed- 

[uid  left 
buor  ob- 
Icommon 
^ount  of 
It  con- 
Id  either 


by  heating  with  manganese  dioxide  and  sulphuric  acid,  or 
by  chlorine.  Most  of  the  bromine  of  commerce  is  not 
obtained  from  sea-water,  however,  but  from  certain  salt 
springs,  which  contain  a  larger  proportion  of  the  element. 
Almost  all  of  the  bromine  used  in  America  (over  half  a 
million  pounds  a  year)  is  obtained  from  brines  found  in 
Ohio,  West  Virginia,  and  Kentucky.  Bromine  or  its 
comp*^  unds  are  used  for  making  dyes,  .also  in  medicine 
and  in  photography. 

Sea-water  contains  only  a  trace  of  iodine  ;  but  some  sea- 
weeds (one  or  two  kinds  in  particular)  have  the  power  of 
extracting  iodine,  which  promotes  their  growth.  From 
kelp,  the  ashes  of  these  seaweeds,  iodine  was  for  a  long 
time  obtained,  and  is  still  to  a  certain  extent  prepared. 
The  iodine  in  the  ash  is  not  far  from  1%  of  the  total 
weight.  Iodine  is  now  largely  obtained  from  Chili,  exist- 
ing in  small  quantity  in  crude  Chili  saltpetre,  which  is 
mainly  sodium  nitrate.  So  much  nitrate  is  required  in 
commerce  tliat  though  the  amount  of  iodine  in  the  crude 
salt  is  comparatively  small,  there  is  more  than  enough  to 
supply  the  demand.  Iodine  and  its  compounds  are  used  in 
medicine  and  in  the  manufacture  of  some  dyes. 

The  similarity  l-etween  the  methods  of  obtaining  chlo- 
rine from  common  salt,  bromine  from  bittern,  and  iodine 
from  the  iodide  in  kelp,  is  sliown  by  the  ecpiations 

2NaCl  +  3H2S()^  +  Mn02  =  2NaHS04  +  MnS04-h2Il2O-f-672 
MgBr2  +  2  ll2S()4  +  Mn02=  MgS04  +  MnS04  +  2  ly)  +  Hi^ 
2NaI  +31l2S()4  +  Mn02=  2NaHS04  +  MnS04  +  2Il2O  +  l2 

The  difference  between  the  second  equation  and  the 
others  in  the  amount  of  sulphuric  acid  used  is  due  to 


122 


CHEMISTRY 


magnesism  not  forming  an  acid  sulphate  similar  to  sodium 
hydrogen  sulphate. 

Chlorine  is  not  only  the  most  important  of  the  three 
elements,  but  it  was  tlie  first  to  be  discovered,  having 
been  prepared  by  the  Swedish  chemist  Scheele  in  1774, 
while  iodine  was  discovered  in  1812  by  Courtois,  a 
Frenchman,  and  bromine  in  182G  b}'  Halard,  also  a 
French  chemist.  Bromine,  in  its  character,  is  between 
chlorine  and  iodine,  and  was  really  obtained  by  Liel)ig 
several  years  before  Balard's  discovery,  but  Liebig,  think- 
ing that  he  was  dealing  with  a  compound  of  chlorine  and 
iodine,  did  not  test  i-he  substance,  thus  losing  the  credit 
of  finding  a  new  element.  Chlorine  is  a  gas,  bromine  a 
liquid,  nearly  three  times  as  heavy  as  water,  and  iodine  a 
solid,  nearly  five  times  as  dense  as  water.  Both  bromine 
and  iodine  may  be  vapourised  by  heat  ;  bromine,  even  at 
ordinary  temperature,  giving  off  considerable  vapour. 
Iodine  melts  on  being  sufficiently  heated,  and  the  liquid 
boils.  But  long  before  ^He  solid  melts  it  gives  off  vapours. 
A  substance  that  gives  off  vapour  without  melting  is  said 
to  sublime.  IMany  substances  sublime  to  a  slight  extent, 
ice,  for  instance,  which  loses  weight,  even  on  a  cold  day 
when  it  does  not  melt;  but  iodine  shows  the  property  of 
subliming  in  a  much  greater  degree. 

Of  the  three  elements  we  are  considering,  chlorine  is 
the  lightest  in  colour,  while  iodine  is  the  darkest;  chlorine 
is  the  nioK.t  ready  to  combine  with  nearly  all  of  the  ele- 
ments, iodine  the  least  ready.  Not  only  is  there  this 
gradation  in  properties,  but  there  is  a  corresponding 
gradation  in  atomic  weiglit.  Chlorine  has  an  atomic 
weight  35.5;  35.5  grammes  of  chlorine  unite  with  one 
gramme  of  hydrogen  to   form   3(3.5  grammes  of   hydro- 


THE  HALOGENS 


123 


0  sodium 

he  three 
,  having 

in  1774, 
Lirtois,  a 
,    also    a 

between 
y  Liel)if];' 
ig,  think- 
)rine  and 
lie  credit 
romine  a 

iodine  a 

bromine 
,  even  at 

1  vapour, 
le  liquid 
vapours. 

is  said 
extent, 
old  day 
Iperty  of 

lorine  is 

chlorine 

Ithe  ele- 

ire  this 

(onding 

atomic 

ith  one 

hydro- 


chloric acid,  represented  by  the  formula  II CI.  The  atomic 
weight  of  bromine  is  80 ;  80  grammes  of  bromine  are 
united  to  one  gramme  of  liydrogen  in  81  grammes  of 
hydrobromic  acid,  represented  by  the  formula  lllir.  Iodine 
lias  an  atomic  weight  127  ;  127  grammes  of  iodine  are 
united  to  one  gramme  of  hydrogen  in  128  grammes  of 
hydriodic  acid,  represented  by  the, formula  III.  How  does 
the  weight  of  all  of  these  gases  compare  with  air  ?  What 
was  your  experience  regarding  the  wciglit  of  chlorine, 
bromine  vaj^our,  and  iodine  vapour  as  compared  with  air? 

Hydrobromic  acid  and  hydriodic  acid  you  have  not 
prepared,  because  they  are  not  important,  and  are  not  so 
easily  prepared  as  hydrochloric  acid.  You  remember 
they  are  not  obtained  in  the  same  way.  Tlie  properties 
of  the  three  acids  are  as  similar  as  those  of  the  three 
salts,  sodium  chloride,  ])romide,  and  iodide.  You  have 
seen  that  the  formuhe  of  tlie  chlorides,  bromides,  and 
iodides  are  exactly  similar,  wdiich  shows  that  the  valency 
of  the  three  elements  is  the  same  in  these  salts.  What  is 
their  valency  in  these  compounds  ?  The  three  elements 
unite  directly  with  metals  to  form  salts  analogous  to 
common  salt,  and  are,  therefore,  called  halogens^  tlie  word 
meaning  "  salt-formers." 

Oxygen  Compounds  of  the  Halogens.  —  Neither  chhuine, 
bromine,  nor  iodine  has  any  great  aflinity  for  oxygen. 
Iodine  is  the  only  one  that  forms  even  moderately  stable 
compounds,  and  these  are  decomposed  hy  heat.  There 
are  compounds  that  contain  hydrogen  and  oxygen,  to- 
gether with  the  halogen,  but  these  compounds  are  not 
very  important.  The  compounds  containing  halogen  and 
oxygen  together  with  a  metal  are  more  important.  Of 
these,  by  far  the  most  important  are  the  hypychlorites  and 


124 


CHEMISTRY 


the  chlorates.  These  may  be  produced  together  with 
chlorides  by  the  action  of  chlorine  on  such  substances  as 
caustic  potash  in  solution.  When  chlorine  acts  on  caustic 
potash  the  action  may  give  potassium  chloride  and  hypo- 
chlorite, or  chloride  and  chlorate,  according  to  circum- 
stances. 

The  action  is  represented  by  the  equations 

2  KOH  +    CVg  =  KCl     +  KCK)    +  Ha^) 

potassium 
hypochlorite 

6  KOH  +  :3  6%  =  5  KCl  +  KClOg  +  3  U^( ) 

potassium 
chlorate 

Potassium  hypochlorite  readily  gives  up  its  oxygen,  and 
is,  therefore,  a  bleaching  agent.  'J'he  compound  "  bleach- 
ing powder"  obtained  by  the  action  of  chlorine  on  lime 
is  much  more  commonly  used.  It  resembles  potassium 
hypochlorite  in  many  respects.  It  is  often  called  chloride 
of  lime.  It  is  used  instead  of  chlorine  water  because  more 
readily  transported  and  more  convenient  to  work  with, 
but  the  principle  of  its  action  is  the  same,  and,  in  fact, 
-r^dorine  is  produced  from  it  in  the  process  of  bleaching. 
The  chloride  of  lime  is  dissolved  in  water,  the  fabric  is 
dipped  into  it  and  afterwards  into  dilute  acid,  and  the 
chlorine  produced  causes  the  l)leaching. 

The  most  important  chlorate  is  potassium  chlorate,  of 
which  you  have  alrendy  had  some  experience.  What  is 
obtained  by  heating  potassium  chlorate? 

The  equation  representing  the  reaction  is 

2KC103  =  2KCl  +  302 

What   volume   is   represented   by   SOg?      How   many 


THE  II A  LOG  ENS 


125 


lier  with 
tances  as 
n  caustic 
nd  hypo- 
I  circuni- 


.() 


^'gen,  and 

"  bleach- 

;  on  lime 

)()tassium 

chloride 

use  more 

)rk  with, 

,  in  fact, 

caching. 

fabric  is 

and  the 

prate,  of 
What  is 


many 


grammes  of  potassium  chlorate  are  required  to  produce 
that  volume  of  oxygen? 

If  potassium  chlorate  is  mixed  with  a  substance  ready 
to  combine  with  oxygen,  tlie  potassium  chlorate  is  still 
more  readily  decomposed  than  when  heated  alone.  A 
mixture  of  potassium  chlorate  and  sugar  explodes  if  placed 
on  an  anvil  and  struck  by  a  hammer.  A  mixture  of 
potassium  chlorate  and  sul[)hur  gives  rise  to  explosions  if 
rubbed  by  a  pestle  in  a  mortar.  A  mortar  is  a  heavy  bowl- 
shai)ed  dish  often  made  of  porcelain,  in  which  substances 
may  be  ground;  iXia  i^eatle  is  the  instrument  with  which 
they  are  ground.  These  experiments  are  probably  too 
dangerous  for  you  to  try. 

When  \  otassium  chlorate  has  strong  sulphuric  acid  put 
upon  it,  a  greenish  yellow  gas,  called  chlorine  peroxide, 
whose  formula  is  ClOg,  is  produced.  It  very  readily 
decomposes  with  explosion,  and  the  experiment  is  a 
dangerous  one.  The  following  experiment  may,  however, 
be  performed  with  safety  : 

Experiment  52.  Grind  some  potassium  chlorate  in  a 
mortar  till  a  tine  powder  is  produced.  Then  grind  sepa- 
rately about  an  equal  quantity  of  white  sugar,  and  mix  the 
two  by  putting  them  upon  paper  and  stirring  them  to- 
gether. Do  not  think  of  mixing  them  in  the  mortar,  as 
they  might  explode  with  the  friction.  Place  the  mixture 
in  a  long  heap,  say  twenty  times  as  long  as  it  is  wide. 
Dip  a  glass  rod  into  sulphuric  aciO  or  take  out  a  drop  in 
a  glass  tube  and  touch  one  end  of  the  heap  with  the  acid. 
You  should  find  that  the  mixture  takes  fire  and  burns 
from  one  end  to  the  other,  so  be  careful.  The  first  so- 
called  "chemical  matches,"  which  were  invented  about 
1812,  were  not  like  our  modern  matches,  but  the  head  was 


12G 


CHEMISTRY 


made  of  a  mixture  of  potassium  clilorate  and  sugar,  and 
they  were  lighted  by  being  dipped  into  sulphuric  acid. 

Fluorine  is  an  element  in  many  respects  similar  to 
chlorine,  bromine,  and  iodine.  It  is  still  more  active  and 
hence  very  difhcult  to  separate  from  its  compounds,  for 
as  soon  as  separated  from  one  substance  it  is  ready  to 
attack  something  else.  Platinum  is  almost  the  only  sub- 
stance not  attacked,  with  the  exception  of  compounds 
such  as  tluorspar,  which  already  have  their  full  amount  of 
fluorine. 


I  gar,  and 
acid, 
niilar  to 
!tive  and 
unds,  for 
ready  to 
)nly  sub- 
mpounds 
mount  of 


CHAPTER    XI 
NITRIC  ACID  AND  THE  OXIDES  OF  NITROGEN 

Nitric  Acid.  —  Experiment  53.  Taste  some  saltpetre. 
Does  it  most  resemble  an  acid,  an  alkali,  or  a  salt  ?  Wliat 
does  it  show  with  litmus  ? 

How  did  you  test  for  the  metal  in  sodium  chloride  and 
potassium  chloride  ?  What  colour  is  given  to  the  flame  by 
saltpetre  ?     AV^hat  is  the  metal  ? 

Preparation  of  Nitric  Acid.  —  Pour  some  strong  sulphuric 
acid  upon  a  little  powdertd  saltpetre  in  a  test-tube. 
What  evidence  have  you  that  an  acid  is  produced  by  the 
action  ?  The  acid  is  nitric  acid.  The  salts  of  nitric  acid 
are  nitrates.  As  a  general  rule  when  the  name  of  an  acid 
ends  in  -ic  the  name  of  the  salt  ends  in  -ate.  Nitrates 
may  be  considered  as  derived  from  nitric  acid  by  replac- 
ing the  hydrogen  of  nitric  acid  by  a  metal ;  or  nitric  acid 
may  be  obtained  from  a  nitrate  by  replacing  the  metal  by 
hydrogen. 

This  action  is  similar  to  that  by  which  hydrochloric  acid 
is  obtained  from  a  chloride.  Just  as  the  action  of  sul- 
phuric acid  on  potassium  chloride  may  be  represented  by 
the  equation 

KCl        +  H28O4  =  KHSO4  -f        JICl. 

potassium  hydrochloric 


chloride 


acid 


127 


128 


CUEMlsrUV 


So  the  action  of  sulphuric  acid  on  potassium  nitrate  may 
be  represented  by  the  equation 

KNO3  +       Il2S()4=     KHSO4      +  IINOg. 

potassium  nitric  acid 

nitrate 

It  is  not  usual  to  speak  of  potassium  lujdrochlorate  as 
the  salt  derived  from  hydrochloric  acid  in  the  same  way  as 
potassium  nitrate  is  spoken  of  as  the  salt  derived  from 
nitric  acid,  because  the  name  potassium  chloride  is 
simpler. 

Compare  the  two  formuhe,  KCl  and  KNOg.  What 
group  of  atoms  in  the  latter  salt  corresponds  to  the  chlo- 
rine atom  in  the  former? 

A  group  of  atoms  which  acts  like  a  single  atom  in  this 
manner  is  called  a  compound  radical.  That  part  of  a  salt 
which  is  not  metal  is  called  a  salt  radical.  A  salt  radical 
may  consist  of  a  single  element,  or  it  may  consist  of  a 
group  of  elements. 

The  formula  HNOg  represents  that  nitric  acid  contains 
oxygen.  This  formula  is  of  course  a  result  of  experiment. 
The  atomic  weight  of  hydrogen  being  unity,  of  nitrogen 
14,  of  oxygen  16,  what  proportion  is  the  weight  of  ox^-gen 
of  the  total  weight  ?  Has  nitrogen,  as  a  general  rule,  a 
very  great  allinity  for  other  substances?  Has  oxygen? 
What  might  you  expect  to  happen  if  a  substance  which 
unites  readily  with  oxygen  be  treated  with  nitric  acid? 

Experiments  with  Nitric  Acid.  —  Expeuimii:nt  54.  Heat 
a  little  powdered  charcoal  in  a  deflagrating  spoon  till  it 
begins  to  glow,  and  allow  a  drop  or  two  of  the  strongest 
nitric  acid  to  fall  upon  it,  being  careful  that  the  acid  does 
not  spurt  upon  you.  You  should  not  pour  the  acid  from 
a  bottle,  but  take  a  very  little  in  a  glass  tube  so  that  you 


rate  may 


(I 

hlorate  as 
lie  way  as 
ived  from 
iloride    is 


3- 


What 
the  chlo- 

im  in  this 
t  of  a  salt 
lit  radical 
isist  of  a 

contains 

Iperiment. 

nitrogen 

[)f  oxygen 

|al  rule,  a 

oxygen  ? 

Ice  which 

acid  ? 

»4.    Heat 

.n  till  it 

;trongest 

Lcid  does 

Icid  from 

that  you 


r\  ."■  -  IT  rlv, 


yiTlilC  ACID  AM)   THE  OXIDES   OF  yiriiOGEN      129 

will   be  sure   not    to   have   too   much   acid.     The   figure 

(Fig.  3(5)  shows  the 

method. 

Experiment  55. 
Pour  into  a  por- 
celain evaporating 
dish  enough  of  the 
strongest  nitric  acid 
to  cover  the  bottom 
(certainly  not  more 
than  I  inch  deep ; 
probably  ^q  inch 
would  be  better). 
Place  in  the  acid  a 
small  piece  of  phos- 
phorus and  then 
stand  quite  a  dis- 
tance away.  The  phosphorus  should  take  fire  and  burn 
very  vigorously,  as  shown  in  Fig.  37,  and  will   probably 

be  spattered  about.  Tiie 
experiment  should  be 
performed  under  a  hood, 
from  which  the  fumes 
are  carried  away  by  a 
strong  draught  and 
which  prevents  the  phos- 
phorus flying  widely 
about.  If  the  acid  form 
too  deep  a  layer  on  the 
bottom  of  the  porcelain 
dish,  the  phosphorus 
will    not     heat     it     so 


Fia,  36 


130 


CIIEMlSTIiV 


readily,  and  will  not  take  lire  so  soon.  Keddish  brown 
fumes  eonie  oft',  as  well  as  the  heavier  white  fumes  of  the 
burning  phosphorus.  The  eharaeter  of  these  red  fumes 
you  will  learn  later.  As  the  burns  produced  by  phos- 
phorus are  very  severe,  too  nuieh  care  cannot  be  taken. 

What  do  you  ol)tain  when  you  neutralise  caustic  soda 
with  hydrochloric  acid  ? 

ExTKiiiMENT  ;')<).  Into  a  porcelain  evaporating  dish, 
put  some  caustic  i)otash  solution  and  add  enough  nitric 
acid  to  make  the  solution  slightly  acid,  then  evaporate  to 
dryness.  Taste  the  solid  i)roduced.  What  is  it?  What 
chemical  tests  could  you  a[)ply  to  iind  out  whether  you 
are  correct  in  your  judgment?  What  way  have  you 
already  used  to  test  for  the  metal  and  the  acid  in  a  salt? 

Compare  the  two  equations 

Na()II  +  IICl  =  NaCl4-Il20 
and  KOlI-f  IlN03=Ki\03  +  H20. 

State  in  words  the  facts  that  these  equations  give  in 
symbols.  Of  course  there  is  water  present  with  the  alkalis 
and  acids,  though  this  fact  is  not  represented  in  the  equa- 
tion. The  equation  does  tell,  however,  whether  there 
is  more  water  before  the  acid  and  alkali  are  mixed  or 
afterwards.     Which  is  the  case? 

Not  onl}^  does  nitric  acid  give  up  oxygen  to  substances 
readily  oxidisable,  but  so  also  does  potassium  nitrate  when 
sudiciently  heated. 

Experiment  57.  Heat  some  potassium  nitrate  in  a  test- 
tube,  and  test  the  gas  produced,  with  a  glowing  splinter. 
What  is  the  action  of  the  gas  on  the  splinter?  Is  the  gas 
coloured  or  colourless?  Bear  this  result  in  mind  in  order 
to  compare  it  with  that  obtained  in  a  later  experiment. 


;h  brown 
les  of  the 
id  fumes 
by  phos- 
tiiken. 
istic  soda 


iig 


dish, 
gh  nitric 
iponite  to 
?  What 
3ther  you 
liave  you 
in  a  salt? 


s  give  in 

he  alkalis 

he  equa- 

er   there 

nixed  or 

ibstances 
late  when 

fen  a  test- 
[splinter. 

the  gas 
I  in  order 

jriment. 


NITlilC  ACID  AM)    THE   OXIDES   OF  MTllOGES      lol 

Now,  keeping  tin-  mouth  of  th'.'  test-tube  turiu'd  from  you, 
into  the  fused  (or  melted)  nitrate,  dro[)  a  little  piece 
of  glowing  chareoal ;  tlie  burnt  end  of  a  niatcli  will  do. 
What  do  you  see?  In  the  same  way  introduce  a  little  sul- 
phur, either  a  small  lumj)  or  some  powder.  What  is  there 
in  the  nitrate  which  makes  the  cond)Ustion  so  energetic? 

It  will  now  be  interesting  to  try  the  action  of  nitric 
acid  on  several  substances,  and  to  maktj  comparisons  with 
the  action  of  some  other  acids. 

ExPKKlMKNT  58.  l*our  some  strong  hydrochloric  acid 
upon  a  little  cupric  oxide.  What  evidence  have  you 
that  action  takes  place  when  tlie  acid  is  put  u[)on  the 
oxide?  Is  there  a  gas  given  off?  Wliat  is  the  colour  of 
the  liquid?  If  you  cannot  see  the  colour  of  the  liquid  on 
account  of  the  black  solid  mixed  with  it,  you  should 
separate  the  two.     How  can  you  do  this? 

Treat  some  cupric  oxide  in  the  same  way  with  nitric 
acid,  and  make  similar  observations.  How  do  the  colours 
of  the  solutions  compare?  Now  dilute  the  cupric  chloride 
solution  with  water,  and  compare  again.  Dilute  the  cupric 
nitrate  solution,  and  compare  once  more.  Does  the  cupric 
chloride  or  the  cupric  nitrate  change  the  more  on  dilution? 
The  action  in  the  two  '.ases  is  represented  by  the  equations 

CuO  +  2  IICl  =  CuCl,  +  H,0 
and  CuO  +  2  HNO3  =  CuCXO^),  +  H2O. 

Judging  by  the  formuUe  given  in  the  equations,  is 
copper  in  these  compounds  a  univalent  or  a  bivalent 
element?  Is  the  compound  radical,  NO3,  univalent  or 
bivalent? 

What  becomes  of  the  hydrogen  in  the  two  acids?  What 
gas  is  given  off  when  hydrochloric  acid  acts  on  zinc?     If 


1^2 


CHEMISTRY 


*^, 


you  do  not  remember,  try  the  experiment.  What  happens 
wlien  hydrochloric  acid  is  put  upon  copper?  Would  the 
equation  written  above  for  the  action  on  the  oxide  need 
to  Ije  changed  merely  by  leaving  out  the  symbol  for  oxy- 
gen on  each  side  ot  the  equation? 

Now  try  the  action  of  nitric  acid  on  copper.  Would 
the  equation  written  above  for  the  action  of  nitric  acid  on 
cupric  oxide  need  to  be  changed  merely  by  leaving  out 
the  symbol  for  oxygen  on  each  side  of  the  equation?  If 
so,  what  would  bo  the  colour  of  the  gas  produced?  What 
is  the  colour  of  tlic  gas  that  you  see  produced? 

Try  the  action  of  nitric  acid  upon  zinc,  using  dilute 
acid  containijig  about  ten  times  as  much  water  as  of  strong 
acid. 

Does  it  give  the  same  gas  as  is  given  by  copper?  What 
is  there  in  nitric  acid  for  which  hydrogen  has  a  great 
aihnity?  Why  h'lould  3'ou  think  it  likely  that  hydrogen 
would  not  be  produced  by  the  action  of  nitric  acid  on  a 
metal  ? 

Experiment  59.  Pour  the  strongest  nitric  acid  upon 
some  granulated  tin.  After  a  minute  or  so  add  about  an 
equal  quantity  of  water  to  the  acid.  Does  weak  or  strong 
nitric  acid  act  most  energetically  upon  tin?  Mix  some 
of  the  white  paste  produced  in  this  reaction  with  lime. 
What  smell  is  obtained?  Assuming  that  3^ou  had  not 
bee!i  told  of  the  composition  of  nitric  acid,  how  would  this 
experiment  prove  that  the  acid  contains  nitrogen?  Would 
it  also  prove  that  hydrogen  exists  in  nitric  acid?  Give 
reann  for  your  answer. 

Pour  dilute  nitric  acid  upon  some  bright  pieces  of  iron 
wire  in. a  test-tube.  Notice  the  effect.  Upon  some  similar 
pieces  of  wire,  pour  the  strongest  nitric  acid.     How  does 


NITRTC:  ACID  jyD   THE  OXIDES   OF  NITIUX^EN     138 


t  happens 
^ould  the 
tide  need 
[  for  oxy- 

Would 
LC  acid  on 
iving  out 
tion?  If 
?     What 

ng  dilute 
of  strong 

?  What 
;  a  great 
hydrogen 
icid  on  a 

cid  upon 
about  an 
3r  strong 

ix  some 

til  lime. 

had  not 
[)uld  this 
Would 

?     Give 

s  of  iron 
e  similar 
!ow  does 


the  two  cases?     N< 


(Id  water  to 


the  action  compare 
the  strong  acid.  How  does  the  action  now  compare  with 
that  observed  when  the  weak  acid  was  poured  directly 
upon  the  iron  in  the  iirst  case  ?  Last  of  all,  with  a  copper 
wire,  touch  (for  a  moment  merely)  tlie  iron  wire  that  is 
not  acted  on,  and  remove  the  copper  wire  at  once  from  the 
liquid.  What  do  you  observe?  The  iron  when  unacted 
upon  in  the  above  instance  is  said  to  be  in  the  passive 
state.  The  cause  of  the  "passive  state"  is  not  known, 
though  there  has  been  a  great  deal  of  speculation  about  it. 

Statement  regarding  the  Occurrence,  Preparation,  and 
Properties  of  Nitric  Acid.  —  Nitric  acid  is  produced  to  a 
slight  extent  by  electrical  dis(;harge  in  the  atmosphere, 
but  its  source  is  practically  fnmi  nitrates.  The  ultimate 
result  of  the  decay  of  organic  matter,  in  so  far  as  the 
nitrogen  is  concerned,  is  the  formation  of  nitrates.  An 
intermediate  step  is  the  formation  of  ammonia.  These 
changes  are  brought  about  by  different  kinds  of  bacteria. 
The  presence  of  nitrates  in  water  points  to  contamination 
with  sewage ;  but  as  the  nitrogen  in  the  sewage  rccpiires 
time  for  its  ccju version  into  nitrate,  the  harmful  parts  of 
the  sewage  have  probably  been  destroyed  by  tlie  time  that 
nitrates  are  found.  Hut  as  this  is  not  certain  to  be  the 
case,  water  containing  much  nitrate  is  suspected,  though 
the  presence  of  ammonia  is  much  more  serious. 

In  most  cases,  the  nitrates  produced  in  the  soil  are  not 
allowed  to  accumulate,  being  washed  out  by  water  or  used 
up  by  growing  plants;  but  in  dry  countries,  nitrates  are 
found  as  a  crust  on  the  surface  of  the  soil,  particularly  in 
the  neighbourhood  of  towns.  Potassium  nitrate,  called 
nitre  or  saltpetre,  is  largely  found  in  India  and  I'^gypt  in 
this  way.     In  Chili  there  are  enormous  beds  of  sodium 


134 


CHEMISTRY 


nitrate  known  as  Chili  saltpetre.  In  this  country  calcium 
nitrate  is  found  in  some  dry  cjwes. 

Nitric  acid  is  produced  on  tlie  large  scale  from  potas- 
sium nitrate  or  sodium  nitrate.  The  following  equa- 
tions rei)rescnt  the  :eaction  by  which  the  nitric  acid  is 

obtained  : 

K:<03+IT2S()4=KHS04  -f-HNOg 

NaNOg  +  II2SO4  =  NaHS04  +  HNOg 

Would  the  weiglit  of  sodium  nitrate  required  to  produce  a 
certain  quantity  of  nitric  acid  be  more  or  less  than  the 
weiglit  of  potassium  nitrate  ?  A  comparison  of  the  two 
equations  just  given  should  enable  you  to  answer  this 
question.  Sodium  nitrate  is  more  difficult  to  purify  than 
potassium  nitrate,  and  therefore  the  latter  was  for  a  long 
time  used  in  making  nitric  acid,  but  now  most  of  the  acid 
prepared,  connnercially  is  obtained  from  sodium  nitrate. 


Fio.  38 

The  sodium  nitrate  is  heated  in  large  retorts  made  of  cast 
iron,  and  the  nitric  acid  is  condensed  in  glass  or  earthen- 
ware jars  as  in  Fig.  38.  Wliat  oi)jection  would  there  be 
to  attempting  to  make  dilute  nitric  acid  in  iron  retorts, 
by  using  nitrate  and  dilute  sulphuric  acid  ?     Why  does 


NITRIC  ACID  AND   THE  OXIDES   OF  NITROGEN      135 


y  calcium 

)m  potas- 
iig  equa- 
c  acid  is 


produce  a 
than  the 
the  two 
swer  this 
rify  than 
or  a  long 
'  the  acid 
I  nitrate. 


of  cast 
earthen- 
there  be 

retorts, 
hy  does 


the  same  objection  not  hold  against  producing  strong 
nitric  acid  in  this  way,  with  the  nitrate  and  strong  sul- 
phuric acid?  The  strongest  nitric  acid  has  a  density  of 
about  1.5.  If  it  is  boiled  it  becomes  weaker,  till  finally  an 
acid  which  contains  ()H%  of  the  pure  acid,  the  remainder 
being  water,  is  left  behind.  This  acid  has  a  constant  boil- 
ing point  123°  C.  and  a  specific  gravity  1.42.  This  con- 
stant composition  and  boiling  point  exist  at  atmospheric 
pressure,  but  vary  when  distillation  is  made  at  other 
pressures.  A  similar  statement  may  also  be  made  about 
hydrochloric  acid  of  constant  boiling  point. 

The  formula  for  nitric  acid  is  MNOg.  One  molecule 
alone  does  not  afPord  enough  hydrogen  to  i)roduce  a  mole- 
cule of  water,  but  two  molecules  contain  sullicient  hydro- 
gen for  the  purpose.  Phosphorus  pentoxide,  which  you 
obtained  by  burning  phosphorus  in  oxygen  or  in  air,  is 
very  ready  to  take  up  water  from  substances  which  con- 
tain oxygen  and  hydrogen.  Phosphorus  pentoxide  takes 
away  water  from  two  molecules  of  nitric  acid,  and  the 
other  parts  of  these  two  molecules  unite  to  form  one  mole- 
cule of  nitrogen  pentoxide,  or  nitric  anhydride.  The 
name  anhydride  is  given  to  an  oxide  which  will  unite 
with  water  to  form  an  acid.  In  this  case  ^^At^s/^/toreV 
anhydride  takes  water  from  nitric  acid  and  })ec()mes 
phosphoric  acid,  and  owing  to  the  loss  of  water  the  nitric 
acid  is  changed  into  nitric  anhydride. 

In  order  to  represent  nitric  acid  as  made  up  of  water 
and  nitric  anhydride,  the  formula  may  be  written  HgC), 
NgOg,  which  is,  for  the  purpose,  a  convenient  form  (though 
it  does  not  represent  the  molecule  as  a  formula  usually 
does).  When  the  comma  is  written  between  the  U^O 
and  the  NjOg,  it  represents  that  the  compound  nitric  acid 


, 


136 


CHEMISTEY 


is  meant,  —  not  that  the  water  and  nitric  anhydride  are 
separated. 
The  equation 

H,0,  N,0,  =  11,0  +  NA 

nitric 
anhydride 

indicates  that  the  compound  is  decomposed  in  some  way, 
and  that  the  water  is  separated  from  the  anhydride. 

Nitric  anhydride  is  a  white  ci/stalline  solid,  which 
readily  unites  with  water  to  form  nitric  acid.  It  is  v  .y 
liable  to  decompose  into  oxygen  and  an  oxide  of  nitrogen 
containing  less  oxygen  than  nitric  anhydride.  It  is  not 
im})ortant  [.ractically,  and  is  introduced  here  mninly  on 
account  of  its  chemical  relationships. 

Oxides  of  Nitrogen  derived  from  Nitric  Acid.  —  Let  us 
consider  more  fully  the  formula  HgO,  NgO^.  You  have 
seen  that  it  is  i)ossible  to  remove  the  water  from  two 
molecules  of  nitric  acid,  thus  obtaining  the  body  nitric 
anhydride  witli  the  formula  NgOg ;  and  that  this  substance 
is  ready  to  decompose  into  oxygen  and  a  lower  oxide  of 
nitrogen  (that  is,  an  oxide  containing  less  oxygen  than 
nitric  anhydride).  It  is  conceivable  that  by  removing 
water  and  oxygen  from  nitric  acid  the  following  bodies 
might  be  obtained : 

N2O4,         N2O3,         N2O2,         N2O,  and  N2. 

Hut  it  does  not  follow  that  because  the  formuhe  can  be 
ivritten  the  substances  can  be  prepared.  As  a  matter  of 
fact,  however,  they  can  be  so  prepared,  with  the  possible 
exception  of  N2O3,  though  they  are  not  usually  obtained 
perfectly  pure.  What  did  you  see  when  nitric  acid  acted 
upon  tin  ?     The  vapour  given  off  was  mainly  a  substance 


NITRIC  ACID  AND   THE  OXIDfJS   OF  NITROGEN     137 


[Iride  are 


ime  way, 

Lie. 

d,   which 

t  is  V  .y 

nitrogen 

It  is  not 

!.<inly  on 

—  Let  us 
-ou  have 
rom  two 
ly  nitric 
ubstance 
oxide  of 
^en  than 
emoving 
bodies 


can  be 
atter  of 
possible 
btained 
d  acted 
bstance 


whose  percentage  composition  corresponds  to  the  formuhi 
N2O4.  What  weight  of  the  gas  woukl  go  into  22.253  litres 
if  the  formula  is  NgO^?  What  weight  would  go  into  22.253 
litres  if  the  formula  is  NOg?  At  a  low  temperature,  e.r/. 
20°  C,  the  vapour  density  correspoiids  to  the  fornuda 
NgO^r  above  150°  C.  the  density  corresponds  to  the  for- 
mula NO2;  30  that  it  i«  evident  that,  on  heating,  one 
molecule  breaks  up  into  two. 

Some  change  visibly  takes  place  in  the  gas,  for  the  colour, 
which  is  light-brown  at  low  temperature,  becomes  almost 
black  at  high  temperature. 

It  has  been  usually  stated,  that  from  nitric  acid  by  its 
action  on  arsenic  trioxide  the  compound  N20g  is  obtained, 
but  some  doubt  has  lately  been  expressed  by  investigators 
in  the  matter,  that  such  is  the  case. 

Copper  produces  mainly  the  compound  wliose  percent- 
age composition  would  be  represented  by  the  formula 
N2O2,  while  the  action  of  zinc  produces  some  of  the  com- 
pound N2().*  Nitrogen  is  obtained  to  a  small  extent  in 
nearly  all  the  reactions  mentioned  al)ove.  'i'he  substances 
have  been  spoken  of  by  symbols  instead  of  by  names, 
since  the  symbols  icadily  show  the  relationship  to  nitric 
acid,  but  it  is  now  necessjirv  to  learn  the  chemical  names. 
These  compounds  of  nitrogen  and  oxygen  give  a  very 
instructive  illustration  of  how  chemical  names  are  fornicd 

*  If  the  nitric  acid  have  a  strength  of  1  :  10  approximately,  a  consider- 
able amount  of  the  compoun  I  N.^O  is  <.')taiMe(l,  wiieroas  if  tlie  strcnj^th 
be  1 :  4,  very  strongly  coloured  iMincs  are  seen,  doubtless  due  to  the  forma- 
tion of  the  compound  with  formula  NO,  which  unites  with  the  oxygen  of 
the  air. 


138 


CHEMISTRY 


■t- 


You  have  learned  that  the  compound  NjOg  is  called 
nitric  anhydride,-  because  when  combined  with  water  it 
gives  nitric  acid.  The  compound  NgOg  when  combined 
with  water  probably  gives  nitrous  acid,  though  the  com- 
pound decomposes  very  rapidly.  It  is  therefore  called 
nitrous  anhydride.  There  are  still  left  the  compounds 
NgO,  N2O2,  and  N2^4.  ^2^\  ^^  called  nitric  oxide,  NgO  is 
called  nitrous  oxi  le,  and  N2^)4  nitrogen  peroxide. 

You  liave  noti'jcd  that  in  the  naming  of  the  five  com- 
pounds the  word  nitric  occurs  twice,  and  the  word  nitrous 
twice.  It  is  important  to  see  how  the  terminations  -ie  and 
-ous  are  applied. 

Of  tlie  two  compounds  ^fi  '^'^^^  ^2^\'  which  has  the 
more  nitrogen  in  proportion?  The  suihx  -ous  is  similar  to 
the  sul'lix  -ose  and  means  "  full  of."  For  example,  verbose 
means  full  of  words,  lachrymose  means  tearful,  or  full  of 
tears,  dolorous  means  full  of  dolour,  or  grief.  So  nitrous 
means  full  of  nitrogen,  and  nitrous  oxide  has  more  nitro- 
gen than  nitric  o.ade.  In  ti)e  same  way,  nitrous  anhy- 
dride contains  more  nitrogen  in  proportion  to  oxygen 
than  nitric  anhydride.* 

There  are  two  chlorides  of  mercury  liaving  the  formula) 
HgCl  and  IlgClg.  Wliieli  is  the  mercuric  chloride,  which 
the  mcrcurous  ?  So  there  are  two  nitrates.  What  would 
be  the  formula  of  mcrcurous  nitrate?  What  the  formula 
of  mercuric  nitrate? 

The  nai  e  peroxide  you  have  already  met,  as  in  the  case 
of  hydrogen  peroxide.     The  prefix  ''per"  is  a  contraction 


*  It  is  ii>>HaJlij  st.atofl  that  nitric  oxide  is  the  oxide  having  more  oxygen, 
nnd  nitrous  oxide  tl»e  one  having  less  oxygen.  This  is  merely  another 
way  of  expressing  the  same  thing,  but  it  does  not  take  into  consideration 


the  meaning  of  the  suflRxos. 


NITRIC  ACID  AND   THE  OXIDES   OF  NITROGEN     139 


is  called 
water  it 
[iombiriecl 
the  com- 
re  called 
mpounds 
e,  NgO  is 

five  com- 
d  nitrous 
IS  -ic  and 

has  the 
jimilar  to 
,  verbose 
)r  full  of 
)  nitrous 
le  nitro- 
is  anhy- 

oxygen 

formula) 
0,  which 
it  would 
formula 

the  case 
traction 

e  oxygen, 
r  another 
ideration 


N2O                Nitrous  oxide 

or 

N^Og  or  NO  Nitric  oxide 

4( 

^203               Nitrous  anhydride 

(C 

^2^^4               Nitrogen  peroxide 

il. 

N2O5               Nitric  anhydride 

ii, 

for  "  super  "  or  "  hyper,"  and  a  peroxide  contains  a  large 
amount  of  oxygen. 

Other  names  are  given  to  the  oxides  of  nitrogen,  formed 
from  the  Greek  numerals  for  one,  two,  three,  etc. 

The  following  list  arranges  the  formuhe  and  names : 

Nitrogen  monoxide. 
Nitrogen  dioxide. 
Nitrocren  trioxide. 
Nitrogen  tetroxide. 
Nitrogen  pentoxide. 

Not  only  can  oxygen  be  taken  from  nitric  acid,  but 
hydrogen  can  be  added,  ammonia  being  produced ;  and  in 
some  of  the  experiments  by  which  the  oxides  of  nitrogen 
are  prepared,  ammonia  is  produced  at  the  same  time. 

By  far  the  most  important  oxides  of  nitrogen  are  nitrous 
and  nitric  oxide. 

Nitrous  Oxide. — Experiment  60.  Put  about  ten  or 
fifteen  grammes  of  ammonium  nitrate  into  a  small  flask  and 
fit  up  as  in  Fig.  39. 

Heat  the  solid  till  it  melts,  moving  the  flame  about 
under  the  flask  so  that  the  heating  will  be  uniform  and 
not  too  great  in  one  place.*  When  the  liquid  begins  to 
boil,  heat  very  carefully,  removing  the  flame  if  necessary 
from  time  to  time.  The  temperature  should  never  be 
higher  than  just  sufficient  to  give  off  the  gas  at  a  reason- 
able rate.  What  evidence  is  there  that  a  little  of  the 
ammonium  nitrate  sublimes  unchanged,  or  tluit  if  it  breaks 
up  into  two  parts,  these  recombine  to  form  the  original 

*  While  h.)ldinp:  the  flame,  tip  the  burner  so  that  the  hand  will  not  be 
beneath  the  tiask  in  case  there  should  be  an  explosion.  An  explosion  ia 
not  liable  to  happen,  but  it  is  best  to  be  on  one's  guard. 


140 


CHEMISTRV 


substance?  What  is  tlie  name  given  to  the  form  of 
decomposition  by  heat  which  is  followed  by  recombination 
on  cooling  ?  Notice  the  evidence  that  water  is  produced 
when  ammonium  nitrate  is  heated.  Collect  several 
cylinders  of  the  gas  which  escapes.     This  is  nitrous  oxide. 


Fig.  31) 


The  ammonium  nitrate,  as  you  saw,  gives  water  and  nitrous 
oxide.     The  reaction  may  be  represented  by  the  equation 

NH4NO3  =  2  HgO  -\-  N^O. 

Assuming  the  formula  NgO  as  correct  for  nitrous  oxide, 
what  would  be  the  weight  of  22.253  litres?  In  this  case 
would  the  ffas  be  liofhter  or  heavier  than  air  ?  What  ex- 
periments  can  you  try  in  order  to  discover  which  is  really 
thv^  case  ?  Try  enough  of  these  experiments  to  satisfy 
yourself  as  to  the  fact. 

Experiment  61.  Shake  up  a  jar  filled  half  with  water 
and  half  with  nitrous  oxide,  covering  the  mouth  of  the  jar 
tightly  with  your  hand.  What  evidence  have  you  that 
nitrous  oxide  is  soluble  in  water?     What  evidence  have 


NITRIC  ACID  AND   THE  OXIDES   OF  NITROGEN      141 


form  of 
ibination 
produced 
several 
lis  oxide. 


nitrous 
equation 


IS  oxide, 
his  case 
hat  ex- 
really 
satisfy 

h  water 
the  jar 
ou  that 
ce  have 


you  that  it  is  not  so  soluble  as  ammonia  or  hydrochloric 
acid? 

Introduce  into  a  jar  of  nitrous  oxide  a  glowing  splinter 
of  wood.  What  happens?  Into  another  jar  introduce  in 
a  deflagrating  spoon  a  little  burning  sulphur  just  as  soon 
as  it  is  lighted  and  before  it  has  begun  to  burn  vigorously. 
Does  it  continue  to  burn  or  does  it  go  out  ?  Allow  it  to 
burn  vigorously  in  the  air  and  then  introduce  it  into  the 
gas.     Is  there  any  difference  now  in  its  behaviour  ? 

Introduce  into  a  cylinder  of  the  gas  some  sodium  in  i 
deflagrating  si)oon.  Does  any  change  take  place  in  the 
sodium  ?  Now  take  it  out  and  heat  until  it  begins  to 
burn,  and  again  introduce  it.  How  does  the  action  com- 
pare in  the  two  cases  ? 

Try  also  what  happens  when  burning  phosphorus  is 
introduced  into  nitrous  oxide. 

If  you  have  any  jars  in  which  you  can  seal  up  the  gas 
so  that  it  may  be  kept  for  several  days,  preserve  a  jar  full 
of  the  gas  for  future  use. 

Nitrous  oxide  is  a  gas  with  a  sweetish  taste.  When 
inhaled  it  first  produces  a  peculiar  kind  of  intoxication 
which  frequently  shows  itself  in  laughter,  and  hence  the 
gas  is  called  "laughing  gas."  Tlie  inhaling  of  a  larger 
quantity  produces  insensibility  to  pain,  and  nitrous  oxide 
is  frequently  employed  by  dentists  for  that  purpose.  It 
is  more  suitable  than  chloroform  for  minor  operations,  be- 
cause the  effects  are  not  lasting.  The  gas  as  usually  made, 
however,  is  liable  to  contain  injurious  impurities,  and  from 
these  it  must  be  purified. 

Nitrous  oxide  is  soluble  in  water  to  a  considerable 
extent,  and  it  is  one  of  the  gases  more  easily  liquefied,  re- 
quiring about  thirty-one  atmospheres  pressure  at  15° C.  and 


142 


CHEMISTRY 


becoming  liquid  under  Jitniospheric  pressure  at  —  92°C. 
It  is  supplied  in  liquid  form  in  iron  cylinders  for  the  use 
of  dentists  and  others. 

Nitrous  oxide  supports  combustion  nearly  as  well  as 
oxygen.  How  could  the  two  gases  be  distinguished  ?  To 
answer  this  question  think  of  all  the  properties  you  know 
in  which  the  gases  are  different. 

When  ammonium  nitrate  is  heated  too  strongly,  it  de- 
composes partially  in  the  manner  represented  by  the 
equation 

2  NH4NO3  =  4  HgO  +  2  i\rO  +  iV^. 


In  this  reaction,  as  well  as  in  that  represented  by  the 
previous  equation,  all  the  products  except  water  are 
gaseous.  How  would  the  volumes  of  the  gases  compare 
in  the  two  cases  ?  What  would  be  the  comj^arative  weight 
of  the  gaseous  products  ?  Why  were  you  warned  not  to 
heat  ammonia  nitrate  to  a  higher  temperature  than  was 
necessary  just  to  evolve  a  gas  ? 

There  are  various  ways  in  which  it  can  be  proved  that 
the  nitrogen  and  oxygen  are  combined  in  the  proportions 

indicated  by  the  formula 
NgO.  One  method  is  to 
place  some  potassium  in  a 
tube  filled  with  the  gas  over 
mercury,  as  shown  in  the 
figure  (Fig.  40),  and  to 
apply  heat  till  the  potas- 
sium burnS:  After  cooling,  the  gas  left  behind  is  found 
to  occupy  the  same  space  as  the  nitrous  oxide  did,  and 
to  consist  of  nitrogen.  But  it  is  known  that  the  weight 
of  a  given  volume  of  nitrous  oxide  is  to  that  of  the  same 


Fig.  40 


NITIilC  ACID   AND   THE  OXIDES   OF  SITUOaKN     143 


-  92°C. 

the  use 

well  as 
B(l  ?  To 
ou  know 

ly,  it  de- 
by    the 


d  bv  the 
jiter  are 
compare 
^e  weight 
3d  not  to 
lian  was 

ved  that 
►portions 
formula 
is  to 
lim  in  a 
eras  over 
in  the 
and  to 
e  potas- 
s  found 
id,  and 
weight 
he  same 


volume  of  nitrogen  as  44  :  28,  therefore  the  weight  of 
oxygen  united  to  tlie  nitrogen  nuist  have  been  16;  and 
the  A\ eight  of  the  nitrogen  is  28;  hence  tlie  formula  of  tlie 
oxide  must  })e  NgO. 

Nitric  Oxide.  —  IOx]»ehiment  ♦)2.  Kit  up  a  flask  or  bottle, 
holding  half  a  litre  or  h'ss,  witli  tliisthj-tube  and  delivery- 
tube  for  a  gas,  as  in  Fig.  41.  Have  all  of  your  jars  or 
cylinders  ready  for  collecting  the  gas,  because  it  should 
be  collected  quickly. 
Into  the  flask  put  a 
quantity  of  coj)per 
filings,  then  add  wa- 
ter till  the  flask  is 
about  one  quarter 
full,  and  then  about 
an  equal  volume  of 
strong  nitric  acid. 
Collect  the  gas  as  it  escapes,  keei)ing  the  first  bottle 
separate  from  the  others.  Notice  the  colour  that  ap- 
pears in  the  generating  flask.  How  about  the  colour  after 
the  gas  has  been  given  off  for  a  little  while  ?  What  evi- 
dence have  you  that  the  colour  of  the  gas  that  you  first  see 
is  not  that  of  the  gas  produced  by  the  action  of  nitric  acid 
on  copper  ?  If  you  do  not  now  understand  why  there  should 
be  a  difference  between  what  you  see  at  first  and  what  you 
see  afterwards,  keep  the  fact  in  mind  and  try  to  discover 
some  reason  as  you  experiment  further  with  the  gas. 
Leaving  aside  the  first  cylinder  or  bottle  of  gas  collected, 
test  the  solubility  of  nitric  oxide  by  shaking  up  with 
water  in  the  same  way  as  you  did  in  the  case  of  nitrous 
oxide.  Which  is  the  more  soluble  of  the  two  gases? 
Try  whether  a  taper  will  burn  in  the  gas. 


Fk;.  41 


144 


CHEMISTRY 


Into  anotlier  cylinder  put  some  Hulplnir  which  is  Imrn- 
ing  vigorously.  J  low  does  the  result  compare  with  that 
obtaincnl  with  nitrous  oxide  ?  Light  a  small  piece  of 
phosphorus  and  immediately  (before  it  begins  to  burn 
vigorously)  introduce  it  into  a  jar  of  nitric  oxide.  Does  it 
continue  to  liurn  or  does  it  go  out  ?  Introduce  a  piece  of 
phosphorus  which  is  burning  vigorously.  What  happens 
this  time  ?  Which  supi)orts  tin;  combustion  the  more 
readily,  nitrous  or  nitric  oxide  ?  Is  it  the  oxygen  or  the 
nitrogen  of  these  compounds  whi(di  supports  combustion? 
Which  has  the  more  oxygen,  nitrous  or  nitric  oxide  ? 
Which  has  the  greater  proportion  of  oxygen,  nitrous  oxide 
or  water  ?  Which  will  best  su})port  the  combustion  of  a 
piece  of  wood  ?  Which  will  best  support  the  combustion 
of  a  piece  of  sodium  ?  Water  does  not  support  the  com- 
bustion of  ordinary  substances  because  the  oxygen  is  so 
firmly  attached  to  the  hydrogen  that  only  a  few  substances 
can  take  it  away,  but  sodium  is  one  of  these  substances, 
and  the  combustion  of  sodium  is  very  vigorous.  In  nitric 
oxide  nitrogen  and  oxygen  are  more  firmly  united  than  in 
nitrous  oxide,  and  it  is  more  difficult  to  separate  them,  but 
when  they  can  be  sej^arated,  as  by  burning  i)hosphorus, 
the  combustion  is  very  vivid.  Pour  a  few  drops  of 
carbon  bisul[)liide*  into  a  jar  of  rutric  oxide,  shake  up  so 
that  the  vapour  of  the  carbon  bisulphide  may  mix  with  the 
gas,  and  apjdy  a  light.  What  is  the  character  of  the 
flame  ?  What  part  of  the  carbon  bisulphide,  if  any,  is  left 
on  the  sides  of  the  jar  ? 

It  has  been  already  stated  that  the  formula  N2O2  repre- 
sents the  percentage  composition  of  the  gas,  but  it  does 

*  Carbon  bisulphide  is  very  inflammable,  and  care  must  be  taken  not 
to  place  the  bottle  near  a  flame. 


is  ])urn- 
ith  that 
piece  of 
to  burn 

Does  it 
l)iece  of 
happens 
le  more 
n  or  the 
justion  ? 

oxide  ? 
us  oxide 
ion  of  a 
iibustion 
he  corn- 
ea is  so 
bstances 
)st{inces, 
[ii  nitric 

than  in 
lem,  but 
sphorus, 
rops  of 
;e  up  so 
^vith  the 
of  the 

y,  is  left 

>2  repre- 
it  does 

;aken  not 


NITIUC  ACID  AM)    THE  OXIDES   OF  XITROnEX     14.") 

not  necessarily  follow  that  this  is  the  proper  inoU'cular 
formula.  If  the  proper  foniuila  is  X( ),  how  many  j^rammes 
of  the  gas  will  go  into  22.258  litres V  Would  it  in  this 
case  be  heavier  or  lighter  than  air  ?  Would  its  weight 
differ  from  that  of  air  by  a  small  or  by  a  large  amount? 
What  would  be  the  case  if  the  formuhi  is  N._,().^/  Try 
some  experiment  uhich  will  decide  tlie  (piestion  as  to 
its  weight.  Be  careful,  however,  not  to  mistake  the 
brown-coloured  fumes  obtained  ])y  the  action  of  air  on 
nitric  oxide  for  the  gas  itself. 

ExPKiUMKNT  63.  Fill  a  pretty  large  cylinder  with 
water  and  invert  it  over  the  pneumatic  trough,  then,  as 
in  Fig.  42,  bring  a  small  vessel  containing  air  beneath  the 


Fia.  42 

mouth  of  the  cylinder  in  such  a  way  as  to  allow  the  air 
to  pass  into  the  cylinder.  The  small  vessel  should  not  be 
more  than  one-eighth  the  size  of  the  larger.  Introduce 
five  measures  of  air  in  this  way  and  marie  the  height  of 
the  water  in  the  cylinder ;  then  introduce  two  measures 


M6 


CHEMISTRY 


of  nitric  oxide.  What  colour  do  you  notice  in  the  cylin- 
der? What  evidence  have  you  that  the  coloured  sub- 
stance is  absorbed  by  the  water?  Does  it  colour  the 
water?  Test  the  water  in  the  cylinder  with  a  piece  of 
litmus-paper.  Is  it  alkaline,  acid,  or  neutral?  If  you  do 
not  find  that  the  coloured  gas  is  rapidly  removed  by  the 
water,  cover  the  mouth  of  the  cylinder  with  your  hand 
and  shake  it,  being  careful  that  gas  does  not  escape  nor  air 
enter,  and  then  put  back  the  cylinder  in  place  over  the 
pneumatic  trougli.  Which  has  the  greater  volume,  the 
air  at  tlie  start  or  the  gas  which  is  left  behind  at  the  end  ? 
Test  the  gas  left  behind  by  a  lighted  match  or  taper. 
You  have  already  met  several  gases  which  affect  the  taper 
in  the  same  way.  How  could  you  tell  which  of  them  it 
is?  What  use  could  you  make  of  your  knowledge  of  the 
gases  originally  taken,  in  helping  you  to  decide  the 
matter?  What  part  of  the  air  was  removed  by  tlie  nitric 
oxide?  Why  were  red  fumes  produced  at  the  beginning 
and  not  afterwards,  in  the  flask  in  which  nitric  oxide  was 
generated?  What  would  be  the  gas  collected  in  the  first 
cylinder  at  the  beginning  of  the  operation  ? 

Make  a  solution  of  ferrous  sulphate  in  water.  Which 
contains  the  more  iron,  ferrous  sulphate  or  ferric  sul- 
pliate?  Pour  the  ferrous  sulphate  solution  into  a  jar  of 
nitric  oxide.  What  colour  is  produced?  Pour  some  of 
tlie  liquid  into  a  test-tube  and  heat.  What  change  takes 
I)lace  in  the  solution  ? 

Into  the  jar  of  nitrous  oxide  wliich  you  have  kept,  intro- 
duce some  nitric  oxide.  What  difference  is  there  between 
nitrous  oxide  and  oxygen  in  the  action  with  nitric  oxide? 

FiUer  the  liquid  in  the  generating  flask  and  evaporate 
to  a  small  bulk,  then  allow  to  cool,  and  collect  the  crystals 


NITItIC  ACID  AND   THE  OXIDES   OF  NITROGEX     147 


lie  cylin- 
red  sub- 
lour  the 
piece  of 
f  you  do 
d  by  the 
lur  hand 
e  nor  air 
over  the 
ume,  the 
the  end? 
)r  taper. 
:he  taper 
■  them  it 
^e  of  the 
cide  tlie 
lie  nitric 

ginning 
side  was 

the  first 

Which 
:ric  sul- 
[i  jar  of 
some  of 
^e  takes 

>t,  intro- 
jetvveen 
oxide? 
aporate 
crystals 


formed.  Dry  some  of  these  on  blotting-paper.  What  is 
the  colour?  Introduce  a  few  crystals  into  a  dry  test-tube 
and  heat.  What  evidence  have  you  that  the  crystals 
contain  water?  Do  the  crystals  retain  their  shape  after 
heating?  The  water  found  in  crystals  apparent I3'  dry  a; 
in  this  substance  is  called  water  of  crystallisation,  the 
salt  not  taking  the  crystalline  form  unless  water  is  ines- 
ent.  What  is  the  colour  of  the  dried  cupric  nitrate? 
Remove  some  of  the  cupric  nitrate  and  dissolve  in  water. 
What  is  the  colour  of  the  solution?  Heat  the  remainder 
of  the  cupric  nitrate  till  fumes  come  off.  What  is  the 
colour  of  the  fumes?  Continue  heating  till  all  fumes  cease 
to  be  evolved.  What  is  the  colour  of  the  residue?  Does 
it  dissolve  in  water?  What  about  the  action  of  hydro- 
chloric acid  and  nitric  acid  upon  it?  What  is  tlie  sub- 
stance? 

The  action  of  nitric  acid  upon  copper  by  which  nitric 
oxide  is  produced  may  be;  represented  by  the  equation 

8  Cu  -f-  8  HNOg  =  8  Cu  (X()3)2  4-  4  H2O  -f  2  NO, 

but  the  nitric  oxide  is  never  perfectly  pure,  and  unless 
care  is  taken  in  the  conditions  a  great  deal  of  impurity 
may  be  present.  For  example,  after  the  action  lias  gone  on 
for  a  considerable  time  and  a  good  deal  of  copper  nitrate 
has  been  produced,  nitrous  oxide  is  formed  to  a  great 
extent,  instead  of  nitric  oxide.  Why  were  you  told  to 
have  all  of  your  vessels  ready  for  collecting  the  gas 
rapidly  ? 

Nitric  oxide  was  first  collected  by  Priestley  in  1772. 
He  called  it  nitrous  air.  It  was  not  till  two  years  after- 
ward that  he  discovered  oxygen,  and  of  course  the  name 
nitric  oxide  was  not  given  until  later  still. 


iii 


148 


CHEMISTRY 


$  i 


It  is  evident  that  nitric  oxide  cannot  be  found  free 
in  nature.  It  can  be  shown  to  contain  nitrogen  and 
oxygen  by  passing  the  gas  over  heated  copper  irt  the 
same  way  as  was  done  with  air,  and  in  fact  any  compound 
or  mixture  of  nitrogen  and  oxygen  may  be  analysed  in 
this  way.  By  weighing  the  copper  before  and  after  heat- 
ing, and  by  measuring  the  gas,  it  may  be  proved  that  the 
action  is  represented  by  the  equation 

2  Cu  +  2  iV'O  =  2  CuO  +  iVa- 

IIow  does  the  volume  of  the  nitrogen  produced  compare 
with  the  volume  of  the  nitric  oxide  used? 

Nitric  oxide  is  very  sparingly  soluble  in  water  and  is 
difficult  to  condense,  the  boiling  point  of  the  liquid  being 
-  153°  C. 

Nitrogen  Trioxide  or  Nitrous  Anhydride.  —  Nitrogen 
trioxide,  to  which  the  formula  Ng^  )3  is  given,  is  difficult 
to  prepare,  being  obtained  only  at  a  low  temperature, 
about  —  20°  C.  It  is  a  liquid  of  an  indigo  blue  colour, 
and  decomposes  readily  into  nitric  oxide  and  nitrogen 
peroxide. 

It  undergoes  decomposition  when  put  into  water,  but 
with  caustic  potash  it  forms  potassium  nitrite.  The  acid 
that  would  correspond  to  potassium  nitrite  would  be 
nitrous  acid.  When  the  name  of  an  acid  ends  in  -oms, 
the  name  of  the  corresponding  salt  eiids  in  -ite. 

The  equation  representing  the  action  of  nitrous  anhy- 
dride on  caustic  potash  is 

2  KOH  4- N2O3  =  2  KNO2 -I- H2O. 

potassium 
nitrite 


NITIiKJ  ACID  AND   THE  OXIDES  OF  NITROdEN      149 


3Uiul  free 
ogen  and 
ir  ir?  the 
3ompound 
alysed  in 
ifter  heat- 
l  that  the 


compare 


er  and  is 
Liid  being 

Nitrogen 
!5  difficult 
perature, 
e  colour, 
nitrogen 


ater,  but 
The  acid 
'ould  be 
in  -OMS, 

IS  anhy- 


The  nitrites  are  somewhat  imj)()rtant,  and  can  be  com- 
paratively easily  obtained,  althougli  the  corresponding  acid 
and  anhydride  so  readily  decompose. 

ExPEiUMENT  64.  Heat  some  potassium  nitrate  in  a  test- 
tube.  Notice  that  it  melts  and  begins  to  boil.  What  is 
the  cause  of  its  boiling?  After  some  time  introduce  a 
glowing  match  into  the  tube. 

What  evidence  have  3'ou  that  a  gas  is  given  off  by  the 
potassium  nitrate  ?     What  is  the  gas  ? 

The  equation  representing  the  reaction  is 

2  KNO3  =  2  KNO2  +  O2. 

Why  is  this  equation  better  than 

KN03  =  KN02  +  0? 

What  vohnne  of  oxygen  is  represented  by  O^  ?  How 
much  potassium  nitrate  would  be  recpiired  to  give  that 
volume  ?  Does  the  phrase  "liow  nuicli  potassium  nitrate  " 
imply  weight  or  volume  ? 

A  dilute  solution  of  potassium  nitrate  mixed  with  a 
dilute  soluticm  of  sulphuric  acid,  if  not  allowed  to  stand 
too  long,  may  be  considered  as  a  solution  of  nitrous  acid, 
IINOg.  Nitrous  acid  readily  takes  up  oxygen,  forming 
nitric  acid. 

ExPEHiMENT  65.  To  a  dilute  solution  of  potassium 
nitrite  and  sulpluiric  acid  add  in  a  small  stream  a  solution 
of  potassium  permanganate.  What  is  tlie  colour  of  the 
permanganate?  How  does  the  nitrite  solution  affect  the 
colour?  Tlie  i)ermaiiganate  is  changed  by  losing  its 
oxygen,  and  the  sulpluiric  acid  present  forms  potassium 
sulpliate  and  manganese  sulphate.  The  equation  a[)pears 
somewhat  complicated, 


150 


CHEMISTRY 


J 


2  KMnO^  +  3  U^HO^  +  5  HNOj  = 
K2SO4  +  2  MnSO^  +  5  HNOg  +  3  HgO. 

But  though  nitrous  acid  may  be  oxidised^  it  may  also  be 
reduced^  for  it  contains  oxygen,  part  of  which  can  be  given 
up  to  substances  requiring  it. 

Wiiich  lias  the  greater  amount  of  oxygen,  nitrous  oxide  or 
nitric  oxide?  Which  did  we  find  best  supports  combustion? 
Whicli  has  the  more  oxygen,  nitrous  acid  or  nitric  acid? 

ExPEiiiMEMT  G6.  Into  a  test-tube  containing  a  dilute 
solution  of  potassium  nitrate  and  potassium  iodide  pour  a 
dilute  solution  of  sulphuric  acid.  Into  another  test-tube 
containing  a  dilute  solution  of  potassium  nitrite  and  potas- 
sium iodide  pour  a  dilute  solution  of  sulphuric  acid. 
What  is  the  appearance  in  each  case  ? 

The  mixture  of  potassium  iodide  and  sulphuric  acid  acts 
like  a  solution  of  hydriodic  acid. 

What  elements  exist  in  hydriodic  acid  ?  Which  of  them 
is  most  ready  to  combine  with  oxygen  ?  Which  colour 
is  produced  by  the  other  component  of  hydriodic  acid? 
In  which  of  the  two  experiments  above  did  oxidation  of 
the  hydriodic  acid  take  place  ?  Which  produced  the  greater 
oxidation  in  the  above  instance,  potassium  nitrate  or  potas- 
sium nitrite?  Which  is  the  more  active  oxidising  agent, 
nitric  acid  or  nitrous  acid  ?  How  do  they  compare  with 
nitrous  oxide  and  nitric  oxide  in  this  respect  ? 

Nitrogen  Peroxide.  —  Experiment  67.  Heat  some  lead 
nitrate  in  a  test-tube  till  coloured  vapours  come  off 
strongly.  Test  the  escaping  vapours  with  a  glowing 
splinter.  What  gas  is  present,  either  free  or  in  an  easily 
decomposable  compound  ?   The  action  is  represented  by  the 

equation        2  Pb  (N03)2  =  2  PbO  +  4  iV^O^  +  Og. 


ai 

b( 

lei 

r( 

th 

di 


NITHIC  ACID  AND   THE  OJ^WES   OF  NITIiOGEy      lol 


y  also  be 
be  given 

oxide  or 
biistioR? 
c  acid  ? 
a  dilute 
e  pour  a 
test-tube 
id  potas- 
'ic   acid. 

acid  acts 

of  them 
colour 
ic  acid? 
ation  of 
greater 
)r  potas- 
g  agent, 
ire  with 


Heat  a  portion  of  the  lefu!  nitrate  till  no  more  fumes 
are  given  off.  What  is  the  colour  of  the  substance  left 
behind  ?  It  is  lead  oxide.  Is  lead  a  univalent  or  a  biva- 
lent element?  What  is  the  name  of  the  compound  rep- 
resented by  the  formula  NOg^  How  does  the  volume  of 
this  gas  compare  with  the  volume  of  the  oxygen  pro- 
duced at  the  same  time? 

You  will  probably  not  separate  the  oxygen  and  the 
nitrogen  peroxide.  The  separation  might  be  made  by 
passing  the  mixed  gases  lurough  a  tube  surrounded  by 
a  freezing  mixture.  One  of  the  gases  would  condense. 
Which  one  must  it  be  ? 

Do  you  have  similar  results  when  you  heat  potassium 
nitrate  and  when  you  heat  lead  nitrate  ?  Would  you 
think  from  the  result  of  your  experiment  that  lead  nitrite 
is  more  or  less  stable  than  potassium  nitrite  ? 

Take  care  to  notice  as  often  i.,s  you  can  whether  salts  of 
potassium  and  sodium  are  more  or  less  stable  than  tlie 
salts  of  other  metals  that  you  come  across.  You  heated 
copper  nitrate  in  a  previous  experiment.  Is  it  more  like 
potassium  nitrate  or  lead  nitrate  ?  If  you  do  not  remem- 
ber, repeat  the  experiment. 

What  arguments  have  been  given  for  writing  the  for- 
mula of  nitrogen  peroxide  as  NOj,  and  not  N2()4? 


me  lead 
)me  off 
flowing 
n  easily 
i  by  the 


CHAPTER   XII 


SULPHUR 


Experiments  with  Sulphur.  —  Experiment  68.  Drop 
a  few  fragments  of  roll  sulphur  or  a  quantity  of  powdered 
sulphur  into  water.  Is  sulphur  heavier  or  lighter  than 
water  ?  Is  there  any  appearance  of  solution  ?  If  sulphur 
is  not  soluble  in  water  or  in  the  saliva,  would  you  expect 
it  to  have  a  taste  ?  Boil  the  water.  Do  you  notice  any 
change  in  colour  of  the  sulphur  ?  Does  it  melt  or  does  it 
remain  solid  ?  Does  boiling  water  appear  to  dissolve  any 
of  the  sulphur  ?  Separate  the  water  from  the  solid  sul- 
phur, and  find  out  whether  the  water  contains  any  sulphur. 
How  can  you  do  this  ?  Would  sulphur  left  in  the  open 
air  evaporate  ?  If  you  have  sulphur  in  lumps,  try  whether 
it  is  brittle  or  malleable,  that  is,  whether  it  breaks  or  is 
flattened  by  hammering. 

Put  some  dry  sulphur  into  a  test-tube  and  heat.  Watch 
it  carefully  till  it  melts.  What  about  the  colour?  If 
you  have  ;.  thermometer  which  registers  up  to  150°  C, 
you  may  try  the  temperature  at  which  the  sulphur  melts, 
but  be  careful  to  take  out  the  thermometer  before  heating 
the  sulphur  much  higher.  How  have  you  already  proved 
that  a  thermometer  which  registers  100°  C.  only  could 
not  be  used  for  determining  the  melting  point  of  sulphur? 
What  is  the  colour  of  the  melted  sulphur  ?  Sliake  the 
test-tube.     Is  the  liquid  thin  and  mobile  like  water,  or 

152 


SULPHUR 


153 


68.      Drop 

f  powdered 

ghter  than 

If  sulphur 

you  expect 

notice  any 

:  or  does  it 

issolve  any 

I  solid  sul- 

y  sulphur. 

the  open 

y  whether 

eaks  or  is 

Watch 
lour?  If 
3  150°  C, 
lur  melts, 
e  heating 
ly  proved 
ily  could 
sulphur  ? 
hake  the 
kvater,  or 


< 


thick  and  viscous  like  molasses?  Now  heat  still  more. 
What  change  do  you  notice  in  the  colour  of  the  sulphur  ? 
From  time  to  time  shake  the  tuhe  and  see  whether  the 
sulphur  retains  its  consistency,  that  is,  whether  it  remains 
just  as  mo])ile  or  just  as  viscous  as  hefore.  Would  you 
naturally  expect  heat  to  make  the  suhstance  more  or  less 
mobile  ?  Is  tlie  actual  fact  wliat  you  would  have  expected  ? 
Keep  on  heating  till  tlie  sulpliur  begins  U)  boil,  which  it 
will  not  do  till  the  temperature  is  higher  tlian  can  be 
measured  by  a  mercury  thermometer.  Xow  allow  the 
liquid  to  cool.  At  one  stage  it  is  so  viscous  that  it  will 
pour  out  of  the  tube  very 
slowly.  At  this  stage  pour 
it  into  Water.  Figure  43 
shows  tlie  operation  on  a 
larger  scale.  The  sulphur 
distilled  in  the  retort  con- 
denses into  lic^uid  form  in 
the  neck,  and  flows  into  a 
vessel  of  water.  Take  out 
of  the  water  the  sulphur 
which  you  have  prepared 
and  examine  its  colour. 
Notice  that  it  does  not  feel 
like  the  original  sulphur.  What  is  the  difference  ?  Keep 
some  of  this  sulphur  for  a  few  days  in  order  to  see  what 
change  takes  place.  Heat  another  portion  in  boiling  water 
for  about  a  quarter  of  an  hour,  and  rub  in  your  fingers  to 
see  how  it  compares  with  what  it  was  before  heating. 

Heat  still  another  quantity  of  sulphur  in  a  wide  test- 
tube,  and  when  it  is  melted  allow  to  cool,  watching  care- 
fully.    Notice  the    crystals  that  form.     They  assume  a 


Fi(i.  4.1 


164 


CHEMISTRY 


Vui.  44 


needle  shape.     You  will  probably  not  be  able  to  see  the 
crystals  for  more  than  a  few  seconds.     Why  ? 

If  you  have  enough  sulphur  for  the  purpose,  heat  25  or 
30  grammes  in  a  clay  crucible  or  any  suitable  vessel, 
preferably  one  that  may  be  broken,  or  a 
beaker  may  be  used  and  the  crystals  exam- 
i\  d  from  the  outside.  Allow  the  melted 
si  t  liu  fo  cool,  and  when  about  one-quarter 
has  Golid!fi'>d,  pierce  two  holes  through  the 
crust  on  top  and  pour  out  the  liquid  por- 
tion. Why  should  there  be  two  holes  ? 
Give  a  reason  why  it  is  better  to  have  them  near  oppo- 
site sides  of  the  vessel,  rather  than  near  each  other  in 
the  middle.  After  the  liquid  is  poured  out,  and  the 
crust  is  broken,  the  appearance  is  sometliing  like  that 
in  the  figure  (Fig.  44).  Examine  the  crystals  and  notice 
their  lustre.  Keep  some  of  the  crystals  for  a  week  or  two 
and  see  if  they  retain  their  lustre  and  colour. 

Dissolve  some  sulphur  in  carbon  bisulphide,  remember- 
ing to  keep  it  away  from  flame,  and  allow  to  evaporate 
slowly.  You  may  find  it  conven- 
ient to  put  the  solution  in  a  test- 
tube.  Would  the  solution  evapo- 
rate more  rapidly  from  a  test-tube 
or  from  a  watcli-glass  ?  Why  ? 
If  you  try  both  methods  you  may 
see  which  gives  the  most  perfectly 
formed  crystals.  Figure  45  gives 
the  form  of  a  single  perfect  crys- 
tal. Are  they  the  same  shape  as 
the  crystals  you  got  by  cooling  the  liquid  sulphur  ?  When 
a  substance  crystallises  in  two  forms,  it  is  called  dimorphous. 


Fia.  45 


$: 


)  see  the 

eat  25  or 
e  vessel, 
:en,  or  a 
lIs  exam- 
e  melted 
3-quarter 
ougli  the 
[uid  por- 
3  holes  ? 
ar  oppo- 
other  ill 
and  tlie 
like  that 
id  notice 
ik  or  two 

member- 
ivaporate 


^    When 

l07'ph0U8, 


SULPHUR 


155 


from  the  Greek  word,  wliicli  means  ''two  forms."  Wliieli 
form  of  sulphnr  remains  nnchanj^ed  the  longer?  Vou 
also  obtained  a  specimen  of  snlpluir  somewhat  like  india 
rubber,  not  crystallised  at  all.  It  is  said  to  be  amorphous 
or  without  form. 

EXPEIMMENT  60.  Into  a  test-tube  put  several  crystals 
of  iron  pyrites,  and  heat.  Why  should  tlie  crystals  decrepi- 
tate^ that  is,  break  up  into  smaller  crystals  witli  a  crackling 
noise?  Would  you  judge  from  this  action  that  pyrites 
is  brittle  or  malleable  ?  Pyrites  is  sometii  os  'uxllcd  *'  fool's 
gold."  Would  a  piece  of  gold  decrepitate?  (iold  would 
act  in  that  respect  like  silver  or  copper,  so  you  could 
experiment  with  one  of  these  metals.  Try  hammering 
some  pyrites  and  see  if  you  were  rig  t  in  your  surmise. 
Heat  the  pyrites  for  a  minute  or  two.  What  evidence 
have  you  that  pyrites  ccmtains  sulphur  ? 

Statement  regarding  the  Occurrence,  Preparation,  and 
Properties  of  Sulphur.  — Sulphur  is  found  in  the  neighbour- 
hood of  volcanoes,  probably  produced,  in  some  instances 
at  least,  b}^  decomposition  of  sulphides,  in  the  same  way 
as  pyrites  was  decomposed  in  your  experiment.  Hy  far 
the  largest  quantity  of  sulphur  in  the  market  is  obtained 
from  mines  in  the  volcanic  regions  of  Sicily.  The  sul[)hur 
is  there  found  mixed  with  earthy  matter,  from  which  it  is 
separated  roughly  by  melting  it  and  allowing  it  to  flow 
away  from  the  unfused  material.  It  is  there  purified  by 
distillation.  The  crude  sulphur  is  heated  in  a  large 
retort,  and  the  vapours  are  led  into  a  large  chamber  as 
shown  in  the  figure  (Fig.  4<)).  The  sulphur  is  first  melted 
in  an  iron  pot,  0,  and  runs  through  a  passage  not  shown 
in  the  figure  to  the  retort  G,  whence^  the  vapours  pass  into 
the  chamber  A.     At  first,  when  the  chamber  is  cool,  the 


150 


CHEMISTRY 


sulphur  vapour  is  condeused  into  solid  material,  just  as  in 
cold  weather  water  vapour  is  condensed  into  snow.  The 
solid  sulphur  thus  ohtained  is  a  fine  powder,  and  is  called 
"tlovvers  of  sulphur."  At  a  later  stage  the  sulphur  col- 
lects in  liquid  form  at  the  bottom  of  the  chamber,  and  is 
run  out  into  moulds,  forming  "roll  sulphur.'' 

The  compounds  of  sulphur  show  that  its  atomic  weight 
is  32,  but  the  density  of  the  vapour  of  boiling  sulphur 

is  96  times  that  of  hydro- 
gen at  the  same  tempera- 
ture ;  therefore  there  must 
be  three  times  as  many 
atoms  in  the  molecule  of 
sulphur  vapour  as  in  the 
molecule  of  hydrogen,  and 
the  molecule  of  the  vapour 
of  sulphur  at  the  boiling 
point  is  represented  by 
the  formula  Sg.  At  a  very 
high  temperature,  for  in- 
stance 1000"  C,  the  density 
of  sulphur  vapour  corre- 
sponds to  the  formula  Sg. 
Sulphur  is  found  not  only  native  but  also  in  combination 
with  many  metals.  The  ores  of  very  many  of  the  ordinary 
metals  are  sulphides,  —  for  instance,  galena  or  lead  sul- 
phide, sphalerite  or  zinc  sulphide,  argentite  or  silver  sul- 
phide ;  while  iron  pyrites  is  a  sulphide  not  much  used  for 
obtainimx  the  metal  and  is  therefore  not  called  an  ore  of 
iron,  though  copper  pyrites,  which  contains  copper,  iron, 
and  sulphur,  is  one  of  the  most  important  sources  of  cop- 
per.      The   sulphates  are    combinations   of   metals   with 


Fig.  46 


SULPIIUIi 


157 


just  as  in 
•w.  The 
is  called 
:)hur  col- 
r,  and  is 

c  weight 
sulphur 
)f  Iiydro- 
tempera- 
lere  must 
as  many 
lecule  of 
us  in  the 
>gen,  and 
e  vapour 
;  boiling 
nted  by 
^t  a  very 
,  for  in- 
)  density 
r  corre- 
lula  Sg. 
bination 
ordinary 
ead  sul- 
ver  sul- 
used  for 
n  ore  of 
er,  iron, 
of  cop- 
lIs    with 


sulphur  and  oxygen  in  the  proper  proportions,  the  most 
abundant  being  gypsum,  which  is  calcium  sul])hate  with 
water  in  addition. 

Refined  sulphur  is  used  in  making  gunpowder  and 
matches  and  for  vulcanising  rubber,  while  crude  sulphur 
is  extensively  used  for  killing  the  germs  wliich  are 
destructive  to  grapes. 

The  specific  gravity  of  the  three  varieties  of  sulphur 
differs  slightly  and  is  not  far  from  2.  One  crystalline 
variety  melts  at  115°  C,  the  other  at  120°('.;  the  licjuid 
boils  at  448°  C. 

Hydrogen  Sulphide.  —  ExrEiiiMKN  r  70.  Mix  seven  parts 
by  weight  (say  grannnes)  of  very  fine  iron  filings  with  four 
parts  by  weight  of  powdered  sulphur.  What  is  the 
action  of  a  magnet  on  iron?  Mow  could  the  iron  and 
sulphur  in  the  mixture  be  separated  ? 

Shake  up  a  portion  of  the  mixture  in  a  test-tube  with 
water  and  allow  to  settle.  Why  do  the  iron  and  sulphur 
form  layers?  Shake  up  another  portion  of  the  mixture 
with  carbon  bisulphide.  Which  of  the  two  substances  is 
the  more  affected?  Heat  the  remainder  of  the  mixture  in 
a  dry  test-tube  till  it  begins  to  glow,  and  then  remove 
from  the  flame.  What  evidence  have  you  that  chemical 
action  goes  on  even  after  removal  from  the  flame  ?  When 
the  substance  is  cool,  take  it  out  of  the  test-tid)e  (you  may 
need  to  break  the  tube)  and  powder  it.  What  evidence 
have  you  from  the  appearance  of  the  substance  that  it  is 
no  longer  a  mixture  of  iron  and  sulphur?  Can  you 
separate  the  two  components  in  the  same  way  as  you  did 
before  the  heating?  Would  the  substance  be  called  a 
compound  or  a  mixture?  The  substance  produced  is 
ferrous  sulphide,  FeS. 


1.58 


C II  KM  IS  THY 


Wlijit  luippt'iis  wlu'ii  sulphuric  acid  acts  on  sodium 
cliloridii?  What  niiglit  you  expect  to  happen  when  sul- 
phuric acid  acts  on  ferrous  sulpliide? 

Laboratory  Preparation  of  Hydrogen  Sulphide  and  Experi- 
ments with  the  Gas.  —  Kxpekimknt  71.  Pour  a  little 
strong  suli)huric  acid  upon  a  small  quantity  of  ferrous 
sul2)hide.  Is  the  action  violent  or  otherwise  ?  Is  there 
effervescence,  as  when  sulphuric  acid  acts  on  sodium 
chlorichi?     Smell  cautiously. 

To  another  small  quantity  of  ferrous  sulphide  add  dilute 
sulphuric  acid  and  compare  results  with  the  action  of 
strong-  acid.  I'errous  sulphate  is  insoluble  in  strong 
sulphuric  acid.  What  bearing*  has  this  fact  upon  the 
experiments  }ou  have  tried? 

Into  a  small  flask  provided  with  a  tliistle-tube  and 
delivery-tube,  put  a  few  lumps  of  ferrous  sulphide  and 
cover  it  with  water.  Pour  down  the  thistle-tube  a 
little  strong  sulphuric  acid,  and  shake.  Add  just  enough 
sul[)huric  acid  to  cause  a  liberal  supply  of  gas,  and 
collect  two  or  three  small  cylinders  of  it  over  warm 
water.  Into  one  cylinder  pour  a  little  cold  water,  place 
the  hand  tightly  over  the  mouth  of  the  cylinder,  and 
shake.  What  evidence  have  you  that  the  gas  is  solu- 
ble in  ct>ld  water  ?  Test  the  solution  with  litmus  to 
see  whether  it  is  acid,  alkaline,  or  neutral.  Boil  some 
of  the  solution  for  a  few  minutes.  Which  smells  the 
more  strongly  of  the  gas,  the  hot  water  or  the  cold  ? 
In  wliich  is  the  gas  the  more  soluble?  Apply  a  lighted 
match  to  another  cylinder.  Does  it  burn  ?  Does  it 
support  combustion?  Hold  a  cold  piece  of  porcelain, 
or,  better  still,  a  porcelain  dish  containing  water,  over 
the  flame.     W^hat  evidence  have  you  that  the  gas  con- 


SULPIIUH 


1  ")*) 


sodium 
then  siil- 

d  Experi- 

•  II  little 

f   ferrous 

Is  tlieie 

sodium 

Lid  dilute 
iction  of 
II  strong 
apou  the 

ube   and 

hide  and 

e-tube    a 

t  enough 

^as,   and 

er  warm 

er,  place 

der,  and 

is  solu- 

tmus   to 

oil  some 

lells  the 

le  cold  ? 

I  lighted 

Does   it 

arcelain, 

er,  over 

■oras  con- 


tains liydrogen?*  What  evidence  have  yon  that  there 
is  sulphur  in  the  gas?  Does  tlie  product  of  tlic  l)urniug 
smell  the  same  as  the  original  gas?  flow  docs  tiic  action 
on  litmus  compare  in  the  two  cases?  It  can  he  proved 
that  tlie  gas  contains  nothing  l)ut  hydrogen  aud  sulphur. 
It  is  hydrogen  sulphide  or,  as  it  is  frc(|ucutly  called, 
sulphuretted  hydrogen. 

It  can  he  decomposed  by  heat,  and  the  hydrogen  })ro- 
duced  has  exactly  the  same  volume  as  the  hydrogen 
sulphide  taken.  Hut  the  molecules  of  hydrogen  consist  (►f 
two  atoms,  therefore  the  molecules  of  hydrogen  sulphide 
must  contain  two  atoms  of  hvdroL''en  because  there  are 
exactly  the  same  number  of  molecules  of  hydrogen  sul- 
phide as  of  hydrogen  in  the  same  volume.  The  forunila 
of  hydrogen  sul})hi(lc  nnist  therefore  be  n2S  or  112^2  ''^' 
H2Sg,  etc.,  and  tlie  evidence  from  the  density  of  the  gas 
is  in  favour  of  the  formula  n2S.  The  reaction  by  wliich 
sulphuretted  hydrogen  is  produced  is  rej)resented  by  th(; 
e(piation 


FeS 

-t-        H2S(>,       = 

=        FeSO^ 

-h 

IhS. 

ferrous 

hydrogen 

ferrous 

hydrogen 

sulphide 

sulphate 

sulphate 

sulphide 

Compare 

with 

2  NaCl 

+       \\^^i\       = 

=      Na2S04 

+ 

2  HCI. 

sod   nn 

hydrogeu 

sodium 

hydrogen 

chloi  ide 

sulphate 

sulphate 

chloride 

Is  sulphur  in  hydrogen  sulphide  a   univalent  or  a  biva- 
lent element?     What  about  the  iron  in  ferrous  sulphide? 
Mix  two  volumes  of  sulphuretted  hydrogen  with  three 

*  If  the  result  of  this  experiment  is  not  very  convincing,  burn  some  of 
the  gas  at  a  jet  and  hold  the  porcelain  dish  over  the  flame. 


160 


CHEMISTRY 


} 


volumes  of  oxygen  and  apply  a  lighted  taper,  taking  care 
to  protect  yourself  from  injury  by  the  explosion.  The 
equation  shows  the  leaction 

2  ff^S  ->■  ;i  O2  =  2  II2O  +  2  SO^. 

At  ordinary  temperatures  how  would  the  volume  of  the 
I)rodu('ts  com|;;ire  with  the  volumes  of  the  original  gases? 
Wiiat   difference   would   there    be    at   a   temperature   of 

iio-^c? 

Experiment  72.*  Pass  sulphuretted  hydrogen  gas 
from  the  delivery-tube  successively  through  a  solution  of 

common  salt,  zinc 
sulphate,  copper  sul- 
phate, and  arsenic 
trioxide,  in  each 
case  adding  a  little 
hydrochloric  acid 
to  the  solution.  No- 
tice which  solutions 
are  changed  in  ap- 
pearance. Which 
sulphides  are  insolu- 
ble in  dilute  hydrochloric  acid  ?  Have  you  really  had 
any  proof  that  the  precipitates  are  sulphides  ?  Filter 
some  of  the  black  precipitate,  and  heat  on  a  piece  of 
porcelain  till  it  dries,  and  afterwards  till  it  becomes 
red  hot  and  gives  off  fumes.  What  are  the  fumes  ? 
Have  you  now  any  proof  that  the    substance   is   a   sul- 

*  F'if^nre  47  shows  an  apparatus  arranged  for  purifying  sulphuretted 
hydrogen  before  passing  it  into  a  sohition  to  be  tested.  The  wash  bottle 
in  the  middle  contains  a  little  water  and  frees  the  gas  from  any  impurity 
carried  over  niechanically  from  the  generating  flask.  You  may  not  find 
it  necessary  to  use  the  wash  bottle. 


Fig.  47 


SULPIIUH 


101 


ing  care 
[1.     The 


ne  of  the 
il  gasf's? 
ature   of 

)gen    gas 
lution  of 
alt,    zinc 
Dpper  sul- 
l    arsenic 
in     each 
Q  a  little 
'ic       acid 
tion.   No- 
solutions 
d  in  ap- 
Which 
re  in  sol  u- 
ally  had 
V     Filter 
piece   of 
becomes 
fumes  ? 
IS   a   sul- 

[jlphuretted 
«ish  bottle 

|iy  impurity 
ly  not  find 


phide  ?  The  precipitates  obtained  by  the  action  of 
sulphuretted  hydrogen  are  usually  sulphides.  Now  add 
to  each  of  the  liquids,  whether  containing  a  precipi- 
tate or  not,  more  than  enough  ammonia  to  neutralise  all 
the  acid.  Which  sulphides  are  insoluble  in  a  liquid 
containing  free  ammonia  ?  A  number  of  other  metals  are 
similar  to  sodium,  zinc,  copper,  and  arsenic,  and  the  experi- 
ment you  have  just  tried  is  an  example  of  what  is  con- 
stantly done  in  the  laboratory.  When  one  wislies  to 
know  what  metal  is  in  a  substance,  it  is  sometimes  [)ossible 
to  separate  the  metal  itself  and  thus  to  identify  it.  For 
instance,  iron  could  be  obtained  from  hematite.  15ut  it 
is  usuidly  much  more  easy  to  produce  a  conq)ou nd  of  the 
metal  which  can  be  easily  recognised  as  a  ('om])ou nd  of 
that  metal,  and  of  no  other,  and  so  in  chemieal  analysis  it 
is  much  more  frequently  the  case  that  substances  are  tested 
by  getting  them  into  the  liquid  form  and  then  adding 
certain  reagents  in  order  to  find  out  tlu*  constituents. 
Ammonia,  for  example,  is  a  good  test  for  eoj)[)er  ;  potassium 
ferrocyanide  is  a  good  test  for  iron.  But  it  is  easily  seen 
that  it  would  be  a  great  trouble  to  apply  each  test  se})a- 
rately  till  the  right  one  was  discovered,  if  one  had  no  idea 
what  metal  to  look  for.  It  has  been  found  very  convenient 
to  use  sulphuretted  hydrogen  to  divide  the  metals  into 
smaller  groups.  Some  metals  give  a  precipitate  with 
liydrogen  sulphide  in  an  acid  solution,  some  give  a  pre- 
cipitate in  an  alkalint;  solution,  and  some  do  not  give  a 
precipitate  in  either  acid,  alkaline,  or  neutral  solution. 
So  it  is  easily  seen  that  the  list  of  metals  is  broken  up  into 
smaller  groups  and  that  by  the  addition  of  sulphuretted 
hydrogen  a  good  deal  may  be  learned.  Hence,  notwith- 
standing the  disagreeable  odour  of  the  gas,  it  is  constantly 


1(32 


CllEMISriiY 


employed  in  an  analytical  laboratory.  After  a  while  one 
becomes  accustomed  to  the  smell  and  does  not  find  it  dis- 
agreeable, and  some  people  even  learn  to  like  it.* 

We  have  seen  that  hyurogen  sul[)hide  has  the  formula 
II2S,  corresponding  to  the  formula  W^O  ;  and  though 
sulphur  and  oxygen  are  so  dissimilar  in  appearance  and 
ii<  physical  properties,  they  forai  compounds  which  have 
nianv  analooies. 

Hydrogen  and  sulphur  may  be  made  to  unite  directly 
by  raising  them  to  the  proper  temperature ;  })ut  the 
reaction  is  not  nearly  so  energetic  as  between  hydrogen 
and  oxygen,  and  the  compound  i)roduccd  is  not  so  stable. 
In  heating  organic  substances  containing  hydrogen  and 
sulphur,  sulphuretted  hydrogen  is  often  produced,  just  as 
in  heating  organic  substances  containing  hydrogen  and 
oxygen,  water  is  often  produced.  Sulphuretted  hydrogen 
is  found  in  tlie  so-called  sulphur  springs,  whose  character- 
istic odour  and  taste  are  due  to  the  presence  of  the  gas  in 
solutitm. 

Sulphuretted  hydrogen  can  be  compressed  into  a  liquid 
at  the  ordinary  temperature  by  a  pressure  of  about  seven- 
teen atmospheres,  and  can  be  li(][uefied  at  atmospheric 
pressure  by  cooling  down  to  —  ()2°C.  It  freezes  at  —  o5°C. 
Suli)huretted  hydrogen  is  poisonous  and  should  not  be 
inhaled,  excei)t  in  very  small  quantities. 

Laboratory  Preparation  of  Sulphur  Dioxide  and  Experi- 
ments with  the  Gas.  —  Kx"eiument  7-3.  Burn  some  sul- 
phur in  a  jar  of  air,  keeping  the  jar  covered  so  as  to 
prevent  the  escape  of  fumes.  Pour  a  little  water  into  the 
jar  and  shakv',  and  in  this  way  obtjiin  a  solution.     Test 

*  The  writer  knew  a  man  vvlio  was  so  fond  of  the  smell  of  the  gas  that 
he  one  time  inhaled  so  much  of  it  from  a  bottle  that  he  fell  insensible. 


SULPHUR 


1G3 


,'hile  one 
id  it  dis- 

forinula 

Uiougli 

nice   and 

ieli  have 

directly 
but  the 
lydrogen 
()  stable. 
>gen  and 
I,  just  as 
gen  and 
lydrogen 
liaracter- 
lie  gas  in 

a  liquid 
it  seven- 
lospheric 

-  o5°C. 
not    be 

I  Experi- 
;onie  sul- 
so  as  to 
into  the 
n.     Test 

lie  gas  that 
eusible. 


,    a 


with  litmus ;  smell.  Add  some  barium  chloride 
with  a  little  hydrochloric  acid,  to  a  portion  of  the  solu- 
tion. To  another  part  of  the  solution  add  a  fifth  of  its 
volume  of  concentrated  (strong)  nitric  acid  and  then 
barium  chloride  solution. 

In  one  case  there  should  be  no  precipitate,  or  only  a 
slight  one;  in  the  other  case  there  should  be  a  white  pre- 
ci[)itate.  The  white  precipitate  is  given  by  sulphuric  a(,'id.* 
The  solution  which  did  not  give  a  preci))itate  was  sulj'liur- 
ous  acid.  Whidi  of  these  acids  has  the  most  sulj)hur  in 
proportion?  Wiiich  the  most  oxygen?  Is  nitric  acid  an 
oxidising  or  a  reducing  agent?  This  reaction  is  very 
important  and  should  be  remend)ered,  as  it  is  made  use 
of  on  the  manufacturinnr  scale. 

What  is  the  action  of  dilute  sul[)huric  acid  on  zinc  ? 
What  is  the  action  of  nitric  acid  on  copper? 

ExPEiiiMKNT  74.  Into  a  Hask,  as  shown  in  the  figure 
(Fig.  48),  put  some  copper  wire  or  iilings,  and  cover  with 
strong  sulphuric  acid.  Heat  carefully  over  a  wire  gauze, 
or,  still  better,  on  a  sand  bath,  an  iron  plate  containing 
sand.  He  very  careful  to  have  the  apparatus  so  arranged 
that  if  the  flask  should  happen  to  break,  the  sulphuric  acid 
would  do  no  harm.  Hot  sulphuric  aci<l  causes  a  terrible 
l)urn.  Notice  the  ebullition  of  gas  and  collect  a  cylinder 
of  it  by  downward  displacement,  covering  the  cylinder 
with  a  glass  plate,  and  make  a  solution  by  passing  a  stream 
of  the  gas  into  water.  Take  gi-eat  care  that  the  water 
does  not  run  back  into  the  strong:  acid. 


"."-I 


*  Such  a  sHKiU  (luantity  of  siilphurio  acid  gives  a  visible  precipitate 
that,  unless  the  (lefla,2;ratin,i;  spoon  is  clean,  some  sulphate  may  he  ])ro- 
(lucetl.  Tlie  sulphur  even  niiiy  pi'  sihly  contain  sonic  snlphatc,  It  is 
possible  that  a  little  sulphur  trio-vidu  may  be  formed  in  the  burning,  and 
it,  with  water,  gives  sulphuric  acid. 


^tm^l: 


ir>4 


CHEMISTRY 


The  reaction  by  which  the  gas  is  made  may  be  repre- 
sented by  the  equation 

Cu+ 2  112804=  CuSO,+ 2  H/)  +  .S'a^. 

What  have  you  learned  about  tlie  spet.itic  gravity  of 
the  gas  ?     Does  it  support  combustion  ?     Does  it  burn  ? 

What  is  the  differ- 
ence between  the 
action  of  nitric  acid 
on  cupric  oxide  and 
on  copper  ?  What 
is  the  difference  be- 
tween the  aition  of 
sulphuric  acid  on 
cupric  oxide  and  on 
c<  pper  ?  Show  that 
in  the  hitter  case 
sulphuric  acid  has 
an  oxidising  action, 
while  in  the  former 
it  has  not. 

Assuming  that 
the  equation  repre- 
sents the  facts,  how 
much  of  the  sulphur  is  obtained  in  the  form  of  sulphur 
dioxide?  What  becomes  of  the  rest  of  the  sulphur?  Is 
the  action  more  like  that  of  dilute  sulphuric  acid  on  zinc 
(u-  of  niti'ic  acid  on  coi)per  ? 

How  .tuiny  atoms  of  oxygen  are  represented  as  existing 
in  a  molecule  of  srlphuric  acid  ?  Mow  many  of  these 
we'll",  be  iv'cessar}  to  combine  with  all  of  the  hydi'ogen  ? 
How  iiuixiy  does  that  leave  for  the  sulphur  ?     In  sulphur 


Fig.  48 


1W^^..»^' 


SULPHUR 


166 


be  repre- 


ravity  of 
it  burn  ? 
le  differ- 
ecn  tlie 
iti'ic  acid 
•xide  and 
'  What 
fence  be- 
Ei<.'tir>n  of 
acid  on 
e  and  on 
how  tliat 
ter  case 
acid  lias 
g  action, 
e  former 


that 


n  rep  re - 
cts,  how 

sulphur 
UU'  ?      Is 

on  zinc 

existing 

of  these 

drogen  ? 

sulphur 


dioxide,  is  there  a  larger  or  smaller  proportion  of  oxygen 
for  the  sulphur  than  in  sulphuric  acid  ?  If  sulphur  dioxide 
were  dissolved  in  water,  would  oxygen  need  to  be  added 
or  to  be  taken  away  in  order  to  produce  sulphuric  acid  ? 
Pour  a  little  iodine  solution  into  some  solution  of  sulphur 
dioxide.  What  is  the  colour  of  the  iodine  solution  ? 
What  is  the  colour  of  the  solution  produced  by  the  addi- 
tion of  it  to  sulphur  dioxide  solution  ?  Add  some  barium 
chloride  and  hydrochloric  acid  to  the  solution  thus  ob- 
tained. What  evidence  have  you  of  tbe  presence  of  sul- 
phuric acid  ?  Sulphurous  acid  in  this  case  takes  up 
oxygen,  and  is  called  a  reducing  agent.  Quantitative 
experiments  show  that  given  the  j)roper  conditions  the 
reaction  is  represented  by  the  equation 

I2  +  2  11/)  -t-  SO2  =  2  HI  -f  ir2SO^. 

How  many  grammes  of  iodine  could  be  decolourised 
by  40  grammes  of  a  one  per  cent  solution  of  snip  .  ir 
dioxide?  What  is  it  that  supplies  oxygen  in  this  r'^;i  - 
tion  ?  What  becomes  of  the  rest  of  the  compound  ;:  >ia 
which  the  oxygen  is  obtained?  Why  is  the  i(jdine  sj^d 
to  be  reduced  ? 

Sulphur  dioxide  in  water  is  sometimes  used  as  a  bleavh- 
ing  agent  for  wool,  straw,  and  other  materials,  for  whici) 
chlorine  is  unsuited.  It  is  also  used  as  a  disinfectant, 
sulphur  being  frequently  ])urned  in  houses  where  there 
has  been  an  infectious  disease. 

That  the  composition  of  the  gas  is  actually  that  wliich 
the  name  inq)lies  may  be  proved  by  experiment. 

ExPEKiMEXT  7").  Fill  with  mercury  a  tube  of  the  shape 
shown  in  the  figure  (Fig.  41>)  and  of  abwut  half-inch  bore, 
and  invert  in  a  trough  containing  mercury.     Introduce  a 


166 


CHEMISTRY 


small  piece  of  sulphur,  and  then  enoup^h  oxygen  to  ap- 
proximately lialf  till  tlie  tuhe.  Put  a  mark  to  show  the 
height  of  the  mercury,  then  heat  the  sul})hur.  Notice 
that  it  hums  and  that  the  mercury  goes  down  in  the  tu])e. 
Why  should  it  do  so  ?     When  the  comhustion  is  complete, 

allow  to  cool  to  the  orisri- 


Flu.  49 


nal  temperature.  The 
volume  should  be  the  same 
as  that  of  tlie  oxygen. 
How  many  atoms  are  there 
in  the  molecule  of  oxy- 
gen  ?  How  many  atoms 
of  oxygen  must  there  be 
in  the  molecule  of  the  compound  })roduced  by  burning 
sulphur  in  oxygen  ?  Does  this  distinguish  ])etween  the 
formula'  S()2,  S2O2,  and  S3()2  .  If  the  formula  is  SO2 
and  the  attnnic  weight  of  sulphur  is  3:2,  how  many 
grammes  of  the  gas  will  go  into  22.253  litres?  How 
many  grammes  will  occupy  the  same  volume  if  the  for- 
mula is  S2O2  ?  The  density  of  sulphur  dioxide  compared 
with  air  as  unity  is  2.2  approximately.  Which  of  the 
above  formuhe  is  the  proper  one  ? 

Sulphur  '^''oxide  can  be  condensed  at  atmospheric  press- 
ure by  cooling  to  —  8°  C,  and  is  easily  kept  in  liquid  form 
in  small  sealeH  ?^lass  tubes  at  the  ordinary  temperature. 
The  solution  of  ulphur  dioxide  in  water  is  practically 
sulphurous  ari'l,  though  the  acid  has  never  been  obtained 
without  water.  The  formula  of  the  acid  would  be  H2SO3, 
and  <  impounds  such  as  potassium  sulphite  KgSOg,  in 
which  hydrogen  is  replaced  by  metals,  are  easily  obtained. 
As  nitrites  are  salts  corresponding  to  nitrous  acid,  so 
sulphites   (contraction   for   sulphurites)   are    salts   corre- 


SULPllUli 


167 


311  to  ap- 
show  the 
.  Notice 
the  tube, 
complete, 
the  origi- 
e.  The 
!  the  same 

oxygen, 
are  there 

of  oxy- 
ly    atoms 

there  ])e 
'  burning 
Aveen  the 
ihi  is  SOo 
)w  many 
^  ?      How 

the  for- 
c'ompared 
ch  of  the 

ric  press- 
\m({  form 
perature. 
ractically 
obtained 
)e  HgSOg, 
VgSOg,  in 
obtained, 
acid,  so 
ts   corre- 


sponding to  sulpliurous  ju'id.  The  sul[)iiites  are  employed 
as  reducing  agents,  nt'iilialising,  for  instance,  excess  of 
chlorine  used  for  bU^aching,  just  as  in  your  experiment 
the  colour  of  iodine  was  discharufed  by  the  action  of 
sulphurous  acid. 

Sulphuric  Acid.  —  Vou  have  used  sulphuric  acid  almost 
from  the;  very  bcj'inninL'"  (»f  ^(»ur  work  in  cliemistrv,  and 
you  have  seen  sonu*thing  of  its  imi)ortancc  in  tlie  labora- 
tory. It  is  quite  as  important  in  industrial  chemistry,  that 
is,  in  the  processes  of  chemical  manufacture  on  the  large 
scale.  In  Great  Britain  alone  l.OUO.UUU  tons  is  produced 
every  year,  and  in  the  United  States  a  still  larger  amount. 
Sulphuric  acid  is  found  to  a  slight  extent  in  volcanic 
regions,  (iypsum  is  found  in  large  (piantities,  but  it  is 
not  easy  to  make  suli)huric  acid  from  it.  Why  could 
you  not  use  hydrochloric  acid  or  nitric  acid  to  drive  out 
the  sulphuric  acid?  Sulphur  burns  in  air,  but  it  forms 
sulphurous  anhydride,  and  that  with  water  would  form  sul- 
phuroas  acid,  while  sulpliuric  acid  contains  more  oxygen. 
This  oxygen  can  be  added  by  allowing  the  sulphurous 
acid  solution  to  stand  in  the  presence  of  air  for  a  long 
time,  say  for  months  or  years,  but  this  is  not  a  practical 
method  of  manufacture. 

Sulphuric  Acid  Manufacture. —  i'he  experiment  you  tried 
of  adding  nitric  acid  to  sulphurt)us  acid  soluiion,  illustrates 
the  method  used  on  the  large  scale.  Sul[)hur  dioxide  is 
produced  either  by  burning  sulphur,  or  by  roasting  (that 
is,  heating  in  the  presence  of  a  large  supply  of  air)  iron 
pyrites,  or  some  other  sulphide. 

The  sulphur  dioxide  is  brought  into  large  chambers 
made  of  lead,  the  cheapest  material  that  will  withstand 
the  actiou  of  the  acid  ;  steam,  air,  ami  nitric  acid  are  also 


108 


CHEMISTRY 


introduced  into  the  lead  chambers.  The  nitric  acid 
oxidises  the  sulphur  dioxide  in  the  presence  of  water,  as 
we  saw  in  our  experiments,  and  is  itself  reduced  to  an 
oxide  of  nitrogen  which  takes  up  more  oxygen  from  air 
introduced  with  it,  and  becomes  a  higher  oxide  of  nitrogen, 
that  is,  an  oxide  containing  a  larger  proportion  of  oxygen. 
This  liigher  oxide  is  again  reduced  by  more  sulphur  dioxide 
iii  the  presence  of  water,  more  sulphuric  acid  is  produced, 
and  more  of  the  lower  oxide  of  nitrogen,  which  again  goes 
through  the  same  round  as  before. 

Theoretically,  therefore,  there  need  be  only  a  small 
amount  of  nitric  acid  introduced  at  the  beginning  of  the 
operation,  and  afterwards  only  a  supply  of  sulphur  dioxide, 
water,  and  air.  Practically,  some  loss  of  the  oxide  of 
nitrogen  occurs,  and  hence  nitric  acid  must  be  constantly 
supplied,  though  not  in  large  quantity. 

The  following  equations  give  an  indication  of  the  char- 
acter of  the  changes  that  occur,  though  they  do  not  rep- 
resent perfectly  the  complicated  course  of  the  reaction : 

2  HNO3  +  2  HgO  +  3  >S'02  =  3  H2SO4  +  2  NO 

N0+  0  =  NO^ 
H2O  +  NO^  +  SO^  =  112804  +  NO 

The  lead  chambers  *  are  very  large,  some  of  them  hav- 
ing a  cai)acity  of  80,000  cubic  feet. 

The  strongest  acid  usually  sold  has  a  density  of  1.84  ; 
chamber  acid  has  a  density  of  1.6,  the  density  of  water 
being  unity.     The  chamber  acid  is  concentrated  by  boiling 

*  The  lead  chamber  must  be  large,  otherwise  the  gases  do  not  mix 
properly.  Such  chambers  are  expensive,  and  lately  towers  of  less 
capacity,  but  with  a  special  arrangement  for  mixing  the  gases,  have  been 
introduced  to  some  extent,  and  with  partial  success. 


itric    acid 

water,  as 

ced  to  an 

from  air 

nitrogen, 

if  oxygen. 

Lir  dioxide 

produced, 

Lgain  goes 

T  a  small 
ing  of  the 
r  dioxide, 
oxide  of 
lonstantly 

< 

the  char- 
not  rep- 
letion : 

TO 


lem  hav- 

of  1.84; 
of  water 
y  boiling 

lo  not  mix 

!rs  of   less 

have  been 


SULPHUR 


169 


in  shallow  lead  pans  till  it  has  a  density  of  1.7.  It  cannot 
be  concentrated  any  farther  in  lead  dishes,  because  stronger 
acid  attacks  lead  ;  hence  it  is  evai)orated  in.  large  glass 
flasks  or  in  platinum  dishes,  as  shown  in   Fig.  50,  or  in 


some  cases  in  cast-iron  stills,  since,  though  dilute  sulphuric 
acid  acts  on  iron,  strong  acid  does  not.  Compare  your 
results  obtained  by  treating  ferrous  sulphide  with  concen- 
trated and  dilute  sulpluiric  acid. 

When  sulphur  dioxide  and  oxygen  are  passed  over 
heated  platinised  *  asbestos,  as  shown  in  Fig.  51,  the  two 
unite  to  produce  sulphur  trioxide  SOg.  Sulphur  trioxide 
uniting  with  water  forms  sulphuric  acid.  The  figure 
represents  a  current  of  air  passing  through  a  solution  of 
sulphur  dioxide,  carrying  some  of  it  to  the  platinised 
asbestos,  where  it  is  changed  to  trioxide,  after  which  it 
is  absorbed  in  w^ater. 

This  method  of  making  sulphuric  acid  has  now  become 

*  Platinised  asbestos  is  prepared  by  moistening  asbestos  in  a  solution  of 
platinic  chloride,  adding  to  it  aniinoniuin  chloride  solution,  drying,  and 
igniting.  The  chloride  is  decomposed,  chlorine  being  given  off,  and 
platinum  remaining  upon  the  asbestos. 


170 


CIIEMISriiY 


of  commercial  importance,  and  may  ultimately  replace  the 
older  method.  It  is  much  simphu*  tliun  tlic  uictliod  with 
lead  chambers,  but  there  were  dillicultics  iu  carry inii^  on  the 
process  on  the  large  scale  which  have  now  been  overcome. 


A P^  ^. 


-.-^ 


%  ^c^y- 


hio.  bi 


Sulphuric  acid  is  often  called  oil  of  vitriol,  because  it 
was  first  made  from  ferrous  sulphate  or  green  vitriol. 

Experiments  with  Sulphuric  Acid.  —  What  evidence  have 
you  had  that  sul[)huric  acid  has  a  great  affinity  for  water? 

Experiment  76.  Heat  a  piece  of  sugar  in  a  dry  test- 
tube.  How  can  you  show  that  water  exists  in  sugar  or 
is  produced  in  the  operation  of  heating  ?  What  is  left 
behind  when  the  water  is  distilled  off?  Is  the  distillation 
of  water  from  sugar  a  case  of  simple  distillation,  or  of 
destructive  distillation  ?  To  another  piece  of  sugar  add 
concentrated  sulphuric  acid.  What  evidence  have  you 
now  that  sulphuric  acid  has  been  effectual  in  removing 


eplace  the 
tliod  witli 
ing  on  the 
overcome. 


suLPnun 


171 


►ocause  it 
:riol. 

Slice  have 
)r  water? 
diy  test- 
sugar  or 
[it  is  left 
stillatioii 
on,  or  of 
11  gar  add 
lave  jou 
'cnioving 


water  from  sugar?  Sugar  ("»utains  hydrogen  and  oxygen 
in  just  tlie  right  proportions  to  form  water,  the  remainder 
of  the  substance  being  charcoal  or  carbon. 

Pour  upon  a  piece  of  wood  in  a  test-tube  some  strong 
sulphuric  acid.  What  is  tlie  effect?  Write  on  paper 
witli  dilute  sulpliuric  acid,  and  hold  above  a  flame  so  as 
to  eva})orate  the  water  from  the  acid,  but  far  enough  away 
that  the  heat  of  the  llame  will  not  l)urn  the  paper. 
W^liat  happens  to  the  paper  where  the  acid  was  put  upon 
it? 

It  can  be  easily  seen  from  the  formula  Il2S()^,  got  as 
the  result  of  anaJj/sis  or  of  sj/iifhesis^  that  sulpliuric  acid 
contains  the  elements  of  water.  At  a  high  temperature 
the  acid  breaks  up  into  two  parts,  water  va2)our  and 
sulphur  trioxide,  II2O  and  SO3.  This  is  what  is  seen 
when  sulphuric  acid  boils.  Ileat  a  few  drops  in  a  tube 
t'U  it  volatilises.  The  fumes  seen  are  sulphur  trioxide. 
Sulphur  trioxide  is  called  sul[)lmric  anhydride,  just  as 
sulphur  dioxide  is  called  sulphurous  anhydride.  What 
is  meant  by  the  term  anhydride? 

Experiment  77.  To  a  solutiim  of  sulphuric  acid  add 
a  dilute  solution  of  caustic  soda  till  the  acid  is  just  neutral. 
How  can  you  tell  when  this  point  is  reached  ?  Evaporate 
the  solution  to  dryness.  What  is  the  substance  left  after 
evaporation  ? 

The  action  is  represented  by  the  equation 

2  NaOII  +  II2SO4  =  Xa2S()4  +  2  II2O. 

Compare  this  with  the  equation  for  the  action  of  hydro- 
chloric acid  and  caustic  soda, 

NaOH  +  HCl  =  NaCl  +  II9O. 


i^^ 

^^^^"5* 
**>,1^, 


IMAGE  EVALUATION 
TEST  TARGET  (MT-S) 


1.0 


I.I 


itt  1^    i2.2 


lU 


■  2.0 

li 


|i.25|U|,.6 

^ 

6"     

» 

^ 


y] 


>' 


/ 


/A 


m 


'/ 


Hiotograpliic 

Sciences 

Corporation 


33  WIST  MAIN  STREET 

^-?MTER,N.Y.  I4SM 

(716)  173-4303 


172 


CHEMISTRY 


How  many  molecules  of  the  alkali  (or  base)  are  required 
for  one  molecule  of  hydrochloric  acid  ?  How  many  for 
one  molecule  of  sulphuric  acid  ?  Hydrochloric  acid  is 
called  a  monobasic  acid,  and  sulphuric  acid  a  dibasic  acid. 

Test  the  sodium  sulphate  with  a  little  barium  chloride 
solution,  adding  a  few  drops  of  hydrochloric  acid.*  Do 
the  same  with  sodium  chloride.  All  soluble  sulphates  act 
in  the  same  way  with  barium  chloride,  and  a  sulphate  is 
distinguished  by  this  test. 

There  are  a  number  of  other  acids  containing  hydrogen, 
sulphur,  and  oxygen,  but  they  are  not  nearly  so  important 
as  sulphurous  acid  and  sulphuric  acid. 


*  The  reason  hydrochloric  acid  is  added  is  that  many  compounds  of 
barium  are  insoluble  in  alkaline  or  neutral  solution,  but  not  in  acid. 


required 
lany  for 
acid  is 
sic  acid, 
cliloride 
:l.*  Do 
lates  act 
^phate  is 

^drogen, 
iportant 


Jounds  of 
icid. 


CHAPTER   XIII 
THE  PHOSPHORUS  GROUP  OF  ELEMENTS 

Experiments  with  Phosphorus.  —  Experiment  78.  Cut 
off  a  small  piece  of  phosphorus  under  water,  and  dry  it 
on  blotting-paper.  Take  the  same  precautions  as  when 
you  were  working  with  phosphorus  befoi'e,  because  burns 
with  phosphorus  are  more  painful  than  ordinary  burns. 

Rub  your  penknife,  or  any  piece  of  iron,  two  or  three 
timet:  quickly  on  a  piece  of  wood,  and  touch  the  phosphorus 
with  it.  Put  a  moistened  paper  in  the  fumes  and  taste 
it.  What  reason  do  you  see  for  burns  produced  by  phos- 
phorus being  specially  painful?  Notice  the  smell  of  the 
fumes  from  phosphorus.  The  odour  is  somewhat  similar 
to  that  of  garlic. 

ExPEUiMENT  79.  Place  a  piece  of  filter-paper  upon 
a  tripod  as  in  the  figure  (Fig.  52),  or  on  the  ring  of  a 
retort  stand.  Dissolve  some  dry  phos- 
phorus in  carbon  bisulphide,  and  pour 
enough  on  the  filter-paper  to  moisten  it. 
Allow  to  stand  for  two  or  three  min- 
utes till  the  carbon  bisulphide  is  evapo- 
rated. The  phosphorus  left  behind 
should  take  fire.  Notice  whether  the  ^__„__,,^ 
paper  takes  fire  from  the  burning  phos-  _      ~ 

phorus.      Which  has  the   greater  sur- 
face, the  small  piece  of  phosphorus  you  dissolved,  or  the 

173 


174 


CHEMISTRY 


paper  moistened  by  its  solution  in  carbon  bisulphide? 
In  which  case  would  the  oxygen  of  the  air  have  a  greater 
opportunity  to  act  on  the  phosphorus  ?  Which  would  you 
expect  to  take  fire  the  more  readily  ? 

Upon  a  piece  of  filter-paper,  in  the  same  way  as  before, 
place  less  than  a  teaspbonful  of  dry  potassium  chlorate 
finely  powdered.  Pour  upon  the  chlorate  enough  of  tlie 
solution  of  phosphorus  in  carbon  bisulphide  to  moisten  it, 
and  allow  to  remain  for  a  few  minutes,  keeping  at  a  dis- 
tance of  several  feet,  because  the  combustion  of  the  phos- 
phorus takes  place  with  explosion.  Why  should  the 
phosphorus  burn  more  violently  when  put  upon  the  potas- 
sium chlorate,  than  when  put  on  paper  alone  ?  What 
experiments  did  you  do  some  time  ago  to  show  the  action 
of  potassium  chlorate  on  combustible  substances  ? 

Experiment  80.     Put  a  piece  of  phosphorus  into  a 

test-tube  with  water, 
as  shown  in  Fig.  53. 
Fit  into  the  te"st-tube 
a  cork  with  a  tube 
drawn  out  to  a  nar- 
row opening.  Boil 
the  water.  Does  the 
phosphorus  melt  be- 
low the  boiling  point 
of  water  or  not  ? 
How  does  it  compare 
-  in  this  respect  with 
sulphur  ?  What  evi- 
dence have  you  that 
phosphorus  vapour  passes  out  through  the  tube  with  the 
steam  ?     If  possible,  do  the  experiment  in  a  dark  room  and 


Fig.  53 


TUE  PHOSPHORUS  GROUP  OF  ELEMENTS         175 


Iphide  ? 
greater 
uld  you 

before, 
olilorate 
1  of  tlie 
isten  it, 
t  a  (lis- 
le plios- 
uld  the 
e  potas- 

What 
e  action 

into  a 
1  water, 
b^ig.  53. 
e'st-tube 
a  tube 
'  a  nar- 
Boil 
)oes  the 
lelt  be- 
g  point 
•  not? 
ompare 
3t  with 
lat  evi- 
ou  that 
ith  the 
om  and 


notice  the  colour  that  appears  at  tlie  opening  from  which  the 
steam  issues.  Withdraw  the  test-tube  from  the  flame  and 
notice  that  air  runs  back  into  the  tube.    How  is  this  shown  ? 

Experiment  81.  Put  a  piece  of  phospliorus  into  a 
cylinder  and  notice  that  it  glows  (this  can  be  seen  only  in 
tlic  dark).  Tlien  dip  a  piece  of  paper  or  ch)th  into 
turpentine  and  introduce  into  the  cylinder  witli  the  phos- 
pliorus. If  the  vapour  of  turpentine  covers  over  the 
pliosphorus,  would  you  expect  the  latter  to  continue  to 
glow  ?  Does  the  phosphorus  continue  to  glow  ?  The 
phosphorus  you  have  been  working  witli  is  ordinarily 
called  yellow  phosphorus.  It  must  be  kept  in  water  to 
prevent  its  catching  fire,  it  dissolves  in  carbon  bisulphide, 
and  it  is  very  poisonous.  There  is  another  form  of  phos- 
phorus with  different  properties. 

Experiment  82.  Into  a  small  bottle  introduce  a  piece 
of  phosphorus,  and  then  a  very  small  fragment  of  iodine, 
taking  care  that  the^  touch.  Cover  the  bottle  loosely. 
In  a  few  moments  there  should  be  a  flash  of  flame.  Pour 
some  water  into  the  bottle  and  wash  out  the  phosphorus. 
What  colour  has  it?  What  other  difference  in  appearance 
has  it?  Does  it  dissolve  in  carbon  bisulphide?  Heat  it  in 
water  and  see  if  it  melts.  Does  it  give  off  the  same  kind 
of  vapour  as  before  when  the  water  is  boiling?  The 
phosphorus  thus  obtained  is  called  red  pliosphorus.  It 
does  not  crystallise,  whereas  yellow  phosphorus  may  l)e 
obtained  in  the  form  of  crystals.  Red  phosphorus  is 
therefore  sometimes  called  amorphous  phosphorus.  It  is 
not  poisonous,*  and  does  not  ignite  so  readily  as  yellow 
phosphorus.     In  this  case  we  have  two  allotropic  forms  of 

*  The  amorphous  phosphorus  should  not  be  tasted,  however,  because 
there  may  be  some  of  the  poisonous  variety  still  remaining. 


176 


CHEMISTRY 


one  element.  What  other  examples  of  allotropic  forms 
have  you  had  ? 

The  vapour  of  phosphorus  weighs  62  times  as  much  as 
the  same  volume  cf  hydrogen,  and  as  the  molecular  weight 
of  hydrogen  is  2,  the  molecular  weight  of  phosphorus  is  124. 
But  it  can  be  proved  that  the  atomic  weight  of  phosphorus 
is  31 ;  therefore  the  molecule  of  phosphorus  vapour  has 
four  atoms,  and  the  formula  is  P^.  We  have  noAV  met 
elements  having  two  atoms  in  the  molecule,  one  which 
contains  three,  one  with  six,  and  one  with  four. 

Hydrogen  Phosphide.  —  Experiment  83.  Fit  up  a  flask 
of  a  capacity  of  about  200  c.c,  as  in  the  figure  (Fig.  54). 


Fig.  54 


Into  the  flask  put  a  few  pieces  of  phosphorus  about  the 
size  of  a  pea,  and  then  put  in  enough  concentrated  solu- 


I 


c  forms 

nuch  as 
•  weight 
sis  124. 

spliorus 
>our  has 
ow  met 
e  which 

3  a  flask 
ig.  54). 


bout  the 
;ed  solu- 


THE  PHOSPHORUS   GROUP  OF  ELEMENTS        177 

tion  of  caustic  soda  to  fill  one-third  of  the  flask.  Pass 
hydrogen  from  the  hydrogen  apparatus  till  the  air  is  all 
driven  out  from  the  flask.*  Stop  the  stream  of  hydro- 
gen and  heat  the  flask  till  gas  comes  off.  Notice  the 
bubbles  which  escape  after  a  time  from  the  tube  which 
dips  under  the  water.  Notice  the  smell,  but  be  careful 
not  to  inhale  the  gas,  for  it  is  very  poisonous,  and  will 
soon  give  a  headache. 
If  the  bubbles  do  not 
take  fire  of  themselves 
w^ien  reaching  the  sur- 
face of  the  water,  apply 
a  light  to  them  in  order 
to  avoid  the  escape  of 
any  of  the  poisonous  gas 
into  the  air.  Before  long, 
the  bubbles  will  take  fire, 
and,  owing  to  the  way  in  ^ 
which  they  escape  from 
the  water  into  the  air, 
the  smoke  has  a  ring 
shape    and    moves    with 

what  is   called   a  vortex 

c 


motion.      If    two    rings 
follow   in   quick    succes- 
sion, you  may  be  able  to  see   the   foremost   ring  widen 
out  and  go  slowly,  while    the    hindmost   ring   becomes 

*  The  apparatus  may  be  so  arranged  that  instead  of  hydrogen  being 
passed  into  the  flask  a  few  drops  of  ether  may  be  added.  Only  a  few 
drops  should  be  added,  else  the  bubbles  of  hydrogen  pliosphide  will  not 
inflame  spontaneously.  Figure  55  is  a  diagrammatic  sketch  showing  this 
arrangement. 


Fig.  55 


178 


CHEMISTRY 


smaller,  goes  faster,  and  passes  through  the  other  ring. 
Of  course,  you  cannot  hope  to  see  this  phenomenon  if 
there  is  a  draught. 

The  gas  produced  in  the  reaction  is  called  hydrogen 
phosphide,  or  phosphine.  It  is,  in  many  respects,  similar 
to  ammonia,  and,  as  the  formula  of  ammonia  is  Nlig,  so 
the  formula  of  phosphine  is  -PM3,  and,  though  phosphine 
is  not  strongly  alkaline  like  ammonia,  it  forms  some  salts 
called  phosphonium  salts  similar  to  ammonium  salts. 
There  is,  for  instance,  phosphonium  iodide,  PH4T,  which 
corresponds  to  annnonium  iodide,  NM^I,  but  it  is  not 
nearly  so  stable,  l>eing  decomposed  by  water. 

Tlie  phosphine  obtained  as  described  is  not  perfectly 
pure.  Perfectly  pure  phosphine  does  not  take  fire  spon- 
taneously. A  small  quantity  of  another  phosphide  of 
hydrogen  gives  it  the  property  of  spontaneous  ignition. 

When  phosphine  is  produced  by  the  action  of  caustic 
soda  on  phosphorus,  a  compound  containing  phospho- 
rus and  sodium,  called  sodium  hypophosphite,  is  left  in 
solution. 

The  reaction  is  for  the  most  part  represented  by  the 
following  equation,  though  some  other  reactions  go  on  to 
a  slight  extent  that  are  not  represented  by  it : 

3  NaOH  -+-  P4  +  3  HgO  =  3  NaH2P02  -I-  PH^. 

sodium  hypophosphite 

What  proportion  of  the  phosphorus  employed  forms 
phosphine? 

Compare  the  two  equations 

2  Pi?3  +  4  O2  =  2  H3PO4 

2P  +  5(9  =  P205.* 

*  Tt  will  be  noticed  by  the  reader  that  these  equations  are  not  molecular, 
and  we  could  not  calculate  volumes  in  the  ordinary  method  from  them. 


I 


ler  ring, 
meiion  if 

lydrogen 
s,  similar 
Nllg,  so 
liosphiiie 
)me  salts 
m  salts. 
4I,  which 
t   is   not 

perfectly 
fire  spon- 
jphide  of 
nition. 
)f  caustic 
phospho- 
is  left  in 

s(l  by  the 
J  go  on  to 


5g. 


ed   lorms 


t  molecular, 
rom  them. 


THE  PHOSPHORUS  GROUP   OF  ELEMENTS         179 

For  which  is  the  more  oxygen  required,  for  the  phos- 
phorus or  for  the  phosphine  containing  the  same  amount 
of  phosphorus  ?  Phosphine  is  said  to  be  a  more  reduced 
product  than  phosphorus.  Why?  On  the  other  hand, 
in  sodium  hypophosphite  the  T:)ho^phorus  is  oxi  lised  to  a 
certain  extent,  so  that  three-fourths  of  the  phosphorus  is 
oxidised  by  the  caustic  soda,  and  one-fourth  is  reduced 
during  the  process.  If,  instead  of  caustic  soda,  lime  mixed 
with  water  is  used,  calcium  hypophosphite  is  obtained,  and 
from  it  hypophosphorous  acid  may  be  prepared,  llypo- 
phosphorous  acid  is  not  volatile,  and  therefore  cannot  be 
prepared  by  distilling  the  salt  with  sulphuric  acid  ;  but 
calcium  sulphate  is  nearly  insoluble,  and  when  calcium 
hypophosphite  in  solution  is  treated  with  sulphuric  acid, 
calcium  sulphate  separates  as  a  solid,  and  the  solution  of 
hypophosphorous  acid  is  obtained.  This  method  of  prepa- 
ration of  acid  is  interesting,  being  different  from  those 
which  you  have  had. 

Phosphoric  Acid.  —  When  phosphorus  is  burned  in  air, 
it  combines  with  oxygen,  forming  phosphorus  pentoxide, 
PgOg.  This  substance,  which  you  have  so  many  times 
seen  as  a  white  smoke,  combines  very  readily  with  water, 
and  forms  phosphoric  acid,  so  that  phosphorus  pentoxide 
is  called  phosphoric  anhydride.  It  can  combine  with 
water  in  three  proportions,  shown  by  the  formulae  HgO, 
P2O5 ;  2  HgO,  P2O5 ;  and  3  HgO,  PgOg.  (Remember  that 
this  mode  of  writing  means  that  the  2  and  3  belong  only 
to  the  HjO,  and  not  to  the  P2O5.)  It  might  be  thought 
that  when  these  acids  are  put  into  a  large  quantity  of 
water  they  would  all  be  the  sam.e,  but  they  are  not.  As 
they  are  all  derived  from  phosphoric  anhydride,  they  are 
all  phosphoric  aoids.     They  may  be  written  HPO3  (which 


180 


CHEMISTRY 


is  just  half  of  H2O,  P2O5),  II4P2O7,  and  H3PO4.  The 
hist  is  the  most  iiiiportaiit.  It  can  be  obtained  in  the 
form  of  Large  crystals  whioli  readily  take  up  water,  and 
are  nearly  always  moist.  The  crystals  are  therefore  said 
to  be  deliquescent.  As  it  is  the  most  important  of  the 
three  pliosphoric  acids,  it  is  called  orthophosphoric  acid, 
tlie  prefix  being  derived  from  a  Greek  word  meaning 
riyht.  In  the  molecule  there  are  three  hydrogen  atoms, 
any  or  all  of  which  may  be  replaced  by  metal,  so  that  there 
are  three  different  salts  of  sodium,  NallgPO^,  NagHPO^, 
and  NugPO^.  Orthophosphoric  acid  is  therefore  a  triha^io, 
acid,  just  as  sulphuric  acid  is  a  (:?ibasic  acid  because  it 
forms  salts  NaHSO^  and  NagSO^.  When  the  hydrogen  is 
not  all  replaced  in  an  acid,  the  salt  is  often  called  an  acid 
salt,  and  it  frequently  reddens  litmus-paper  ;  thus  sodic 
hydric  sulphate,  NallSO^,  reddens  litmus.  In  the  same 
way,  sodic  dihydric  phosphate  (wliat  is  the  meaning  of  the 
term?),  NaH2P()4,  is  acid,  but  disodic  hydric  phosphate, 
tliough  its  formula  represents  an  acid  salt,  does  not  redden 
litmus  nor  turn  it  blue,  and  is,  therefore,  a  neutral  phos- 
phate, while  trisodic  phosphate  is  alkaline. 

One  atom  of  calcium  is  equivalent  to  two  atoms  of 
sodium,  as  is  shown  by  the  formula  NaCl  for  sodium  chlo- 
ride, and  CaCl2  for  calcium  chloride  ;  therefore  the  cal- 
cium salt  which  corresponds  to  ^allgPO^  is  CaH4P20g,  or, 
as  it  is  frequently  written,  Call^  (^0^^.  This  calcium 
acid  phosphate,  commercially  known  as  superphosphate  of 
lime,  is  an  important  substance,  being  used  very  largely 
as  a  fertiliser.  The  substance  €33(1^04)2,  corresponding  to 
NagPO^,  is  a  common  mineral,  and  the  reason  why  it  is  not 
used  as  a  fertiliser  is  because  it  is  not  soluble  in  water,  and 
plants  cannot  make  use  of  food  except  as  gas  or  in  solution. 


TIIK  PllOSPIJOIil'S  filiOLP  OF  KLEMESTS         181 


(\.      The 

d  in  the 
^ater,  and 
efore  said 
nt  of  tlie 
oric  acid, 

meaning 
en  atoms, 
that  there 

a  fr?  basic 
jecaiise  it 
^drogen  is 
3d  an  acid 
;hus  sodic 

the  same 
ing  of  the 
)hosphate, 
lot  redden 
itral  phos- 

atoms  of 
iium  chlo- 
3  the  cal- 
^PgOg,  or, 
s  calcium 
)spliate  of 
[■y  largely 
londing  to 
y  it  is  not 
vater,  and 
I  solution. 


Action  of  Heat  on  Phosphoric  Acid.  —  When  orthophos- 
phoric  acid  is  heated  to  a  little  over  200°  C\,  it  loses  water, 
and  is  changed  into  another  acid  called  i)yrophosphonc 
acid,  because  produced  by  heat,  the  prefix  i)eing  deri .  d 
from  the  Greek  word  for  fire. 

3  H2O,  P2O5  =  llgO  +  2  H2O,  P2O5. 

orthophosphoric  acid         pyrophosphoric  acid 

4 

This  has  different  physical  i)n)perties  from  orthophos- 
phoric  acid, — having  a  different  specific  gravity,  for 
instance,  —  and  it  gives  different  results  with  various 
chemical  reagents. 

When  pyrophosphoric  acid  is  heated  still  more  strongly, 

so  that  the  dish  becomes  red,  more  water  is  lost,  and  a 

substance  is  left  behind  called  metaphos[)hoi'ic  acid.     The 

prefix  meta  indicates  that  it  is  an  acid  in  addition  to  the 

others. 

2  H2O,  P2O5  =  H2O  +  H2O,  P2O5. 

metaphosphoric 
acid 

We  do  not  really  know  what  the  molecule  of  the  p-sos- 
phoric  acids  is,  and  we  write  H3PO4,  W^V^i)^^  and  HPOg, 
or  3  II2O,  ]%( V  2  H2O,  P2O5,  and  H2O,  l^O^,  just  to  suit 
our  convenience  for  the  purpose  we  have  in  view ;  some 
of  the  chemical  relations  being  shown  better  by  one 
formula,  and  some  by  another.  The  last  form,  for  exam- 
ple, is  best,  if  we  wish  to  sliow  the  acids  as  compounds 
of  phosphoric  anhydride  with  water. 

No  amount  of  heat  will  drive  off  the  last  portion  of 
water  from  metaphosphoric  acid,  so  that  we  see  again  how 
firmly  phosphoric  anhydride  unites  with  water,  because 
sulphuric  acid,  even  though  having  so  great  an  affinity 


182 


CHEMISTRY 


for  water,  can  be  broken  up  by  heat  into  water  vapour  and 
sulphuric  anhydride. 

Phosphorous  and  Hypophosphorous  Adds.  — In  all  of  the 
phosphoric  acids  there  is  just  the  same  amount  of  oxygen 
for  the  phosphorus,  because  they  are  all  derived  from  the  one 
anhydride  ^^2^\'  ^^^^  there  are  other  acids  of  phosphorus 
which  contain  less  oxygen,  and,  therefore,  more  phosphorus 
in  proportion.  What  would  you  expect  an  acid  to  be 
called  which  contains  more  phosphorus  than  ph()S[)horic 
acid  ?  Orthophosphoric  acid  has  the  formula  W^V^  ^^  ;  phos- 
phorous acid  has  the  formuhi  HgPOg.  We  have  already 
learned  about  hypophosphorous  acid,  which  contains  less 
oxygen  than  phosphorous  acid,  as  is  implied  by  the  prefix. 
Its  formuhi  is  HgPOg.  Phosphorous  acid,  as  well  as  hypo- 
phosphorous acid,  is  ready  to  take  up  oxygen  and  become 
phosphoric  acid,  and  is  therefore  a  reducing  agent. 

Statement  regarding  the  Occurrence,  Preparation,  and 
Properties  of  Phosphorus.  —  Since  hypophosphorous  and 
phosphorous  acids  are  so  ready  to  take  up  oxygen,  they  are 
never  found  in  nature,  and  since  phosphoric  acid  is  a 
strong  acid  it  also  does  not  occur  naturally  uncombined, 
but  the  phosphates  are  very  important  compounds.  Cal- 
cium phosphate  ^^'AJj^O^^,  usually  combined  with  fluoride, 
is  the  most  common  and  the  most  important.  Phosphorus 
is  made  from  it  or  from  the  calcium  phosphate  which 
forms  the  larger  portion  of  bone  ash,  the  residue  left  when 
all  of  the  organic  matter  is  burnt  off  from  bones. 

Though  phosphorus  was  discovered  about  1675,  it  was 
obtained  by  a  very  difficult  process,  and  was  for  a  century 
onl}^  a  curiosity.  In  1775  Scheele,  the  same  man  who 
discovered  chlorine,  made  it  from  bone  ash  by  a  process 
which,  till  latel}^  has  been  exclusively  used.     The  process 


pour  and 

ill  of  the 
f  oxygen 
m  the  one 
losphorus 
losphorus 
lid  to  be 
losphoric 
)^  ;  phos^ 
e  already 
tains  less 
le  prefix, 
as  hypo- 
1  become 
it. 

ion,  and 
rous  and 
,  they  are 
acid  is  a 
ombined, 
lIs.  Cal- 
i  fluoride, 
losphorus 
be  which 
left  when 

5,  it  was 
I  century 
nan  who 
a  process 
e  process 


TUE  puospnoiars  ghovp  of  elemests      188 

is  complicated,  and  is  being  now  replaced  by  heating  the 
phosphate  with  carbon  in  an  electric  furnace.  At  that 
very  high  temperature  carbon  is  able  to  take  oxygen  from 
the  phosphorus,  the  phosphorus  distils  in  the  form  of 
vapour,  and  is  condensed.  The  ordinary  or  yeUow  phos- 
phorus has  a  specific  gravity  1.82,  melts  at  43°  C.  under 
water,  and  more  easily  when  dry,  and  distils  at  209°  C. 
It  is  very  poisonous,  0.15  grammes  being  a  fatal  dose. 
Workmen  employed  in  factories  where  it  is  made  or  used 
are  liable  to  decay  of  the  Ixiucs,  so  that  the  industry  is 
a  very  unhealthy  one.  Ued  or  amorplious  phospiiorus 
made  by  heating  ordinary  phosphorus  in  an  atmosphere  of 
nitrogen  to  a  temperature  of  250°  ('.,  has  a  si)eciiic  gravity 
2.25.  It  is  not  aft'ected  by  air  at  the  ordinary  tempera- 
ture, and  so  does  not  need  to  be  kept  under  water.  At  a 
moderately  high  temperature,  which  varies  according  to 
circumstances,  it  changes  into  the  yellow  modification. 

Phosphorus  is  largely  used  in  the  manufacture  of 
matches.  Friction  matches  were  first  made  in  1827, 
originally  without  phosphorus,  but  very  soon  phosphorus 
was  introduced.  The  tips  of  matches  usually  contain 
phosphorus  mixed  with  some  oxidising  substance.  With 
glue,  and  with  some  neutral  substance.  The  mixture 
must  be  such  as  to  ignite  with  the  proper  amount  of 
friction,  but  not  to  be  too  readily  inflamed.  Since  yellow 
phosphorus  is  poisonous,  and  is  also  readily  inflammable, 
safety  matches  are  made  having  no  phosphoius  in  the 
composition  of  the  heads  of  the  matches  themselves, 
but  having  red  phosphorus  in  the  composition  on  the 
surface  of  the  box.  The  matches  take  fire  only  when 
rubbed  upon  the  prepared  surface. 

In   France,   phosphorus  has  been  lately   replaced  by 


184 


CHEMISTRY 


phosphorus  sulphide,  which  is  said  to  be  much  superior  to 
phosphorus  iilone,  because  not  poisonous.  The  French 
government  offered  a  prize  for  the  best  substitute  for 
phosphorus  in  the  manufacture  of  matches,  and  the  reward 
was  given  for  the  proposal  to  use  pl^osphorus  sulphide. 

Arsenic.  —  Experiment  84.     Into  a  closed  glass  tu])e, 
as  shown  in  Fig.  56,  of  less  tnan  half  a  centimetre  bore 
^-^       and  two  v)r  three  centimetres  lengtli,  put  a  small 
I  I       fragment  of  arsenic  trioxide  (say  the  size  of  a  pin 
head),  and  then  a  piece  of  charcoal  small  enough 
to  allow  it  to  slip  down  the  tube  easily,  but  large 
enough  neaily  to  block  the  i)assage.      Heat  the 
charcoal  till  it  is  red,  then  heat  the  arsenic  tri- 
oxide.    Notice  in  the  tube  a  ring  of  bright  metal- 
lic lustre  forming  a  mirror.     What  substance  do 
you  already  know  for  which  carbon  has  a  great 
alHnity  ?     The  mirror  is  formed  of  the  element 
arsenic  ;    the  trioxide,  often  called  white  arsenic, 
'     is  a  compound  of  arsenic  and  oxygen,  Avhose  com- 
position corresponds  to  the  formula  AS2O3.     The 
element  arsenic  has  a  metallic  appearance,  though 
in  many  respects  it  is  unlike  a  metal. 

Exi»EHiMENT  85.  Put  a  little  powdered  arsenic 
trioxide  into  water.  Does  it  dissolve  readily  ?  Does  it  dis- 
solve at  all  ?  In  order  to  answer  this  question,  filter,  and 
divide  the  filtrate  into  two  parts.  Pass  a  stream  of  sul- 
phuretted hydrogen  througli  one  portion  for  a  couple  of 
minutes.  Is  there  any  precipitate  ?  To  the  other  portion 
of  the  filtrate  add  hydrochloric  acid,  and  then  pass  sul- 
phuretted hydrogen  as  before.  Is  there  a  i)recipitate  ? 
Heat  both  liquids.  Make  a  comi)arison  between  your 
results  in  all  stages  of  your  parallel  experiments. 


THE  PHOSPHORUS  GROUP  OF  i^LEMENTS 


185 


superior  to 
he  French 
stitute  for 
the  reWfird 
Lilphide. 
ghiss  tube, 
net  re  bore 
ut  a  snijiU 
ze  of  a  pin 
all  enough 
,  but  large 
Heat  the 
.rsenic  tri- 
ght  nietal- 
bstance  do 
as  a  great 
le  element 
ite  arsenic, 
^^hose  com- 
igOg.  The 
ce,  though 


red  arsenic 
Does  it  dis- 
filter,  and 
ini  of  sul- 
,  c()Ui)le  of 
ler  portion 
I  pass  sul- 
recipitate  ? 
veen  your 
nts. 


Arsenic  trioxide  has  the  percentage  composition  corre- 
sponding to  the  formula  AsgOg.  Assmniiig  the  atomic 
weight  of  arsenic  as  75,  wliat  wtMght  of  vapour  of 
the  trioxide  should  go  into  22.253  litres,  if  the  substance 
could  be  obtained  as  vapour  having  atmospheric  pressure  at 
0°  C?  It  is  found  by  experiment  tiuit  the  vapour  is  11)8 
times  as  heavy  as  hydrogen  at  the  same  temperature. 
Does  this  correspond  to  the  formula  As2()3  or  As^Og? 

Arsenic  trioxide  docs  not  readily  cond)ine  with  water, 
but  there  are  salts  which  would  correspond  to  an  acid  so 
obtained,  and  hence  arsenic  trioxide  is  often  calle(]  arseni- 
ous  anhydride  and  the  salts  are  arsenites.  A  correspond- 
ing oxide  of  phosphorus  is  known,  but  is  unimportant, 
while  arsenic  pentoxide,  AsgO^^,  wliich  corresponds  to  pnos- 
phorus  [Hmtoxide,  l^^)^,  is  much  less  stable  than  the  latter 
and  readily  decomposes  into  arsenic  trioxide  and  oxygen, 
so  that  the  phosphorus  and  arsenic  oxides  do  not  corre- 
spond as  regards  stability.  Phosphates  and  arsenates  are, 
however,  very  similar  in  their  chemical  relations. 

White  arsenic  is  very  poisonous,  the  fatal  dose  being 
about  the  same  as  that  of  phosphorus.  In  v<*ry  small 
doses,  such  as  ^^  of  a  grain,  it  is  used  as  a  medicine.  It 
has  a  good  effect  on  the  skin  and  on  the  digestion,  but  it 
should  never  be  taken  unless  by  a  doctor's  advice.  The 
habit  grows,  and  as  the  system  becomes  accustomed  to  its 
use,  larger  doses  can  be  taken.  Hut  if  tlie  attem[)t  is 
made  to  discontinue  its  use,  all  tlie  effects  of  arsenical 
poisoning  are  exi)erienced.  Peasants  in  mountainous  dis- 
tricts sometimes  use  ars(*ni(!  in  order  to  strengthen  their 
power  of  breathing  when  c]iml)ing.  It  is  oik;  of  the 
poisons  most  frequently  administered,  probably  because  it 
is  almost  tasteless.     It  is,  however,  one  of  the  most  easily 


186 


CHEMISTRY 


detected.  It  preserves  the  tissues  of  the  stomach  and 
may  be  detected  years  after  the  death  of  the  poisoned 
person.  The  best  antidote  for  arsenic  is  a  mixture  of 
magnesia  and  ferric  hydroxide,  because  arsenic  forms  an 
insoluble  compound  with  these  substances. 

Experiment  86.  Make  hydrogen  in  the  usual  way 
with  zinc  and  sulphuric  acid,  the  delivery-tube  being  in 
the  form  shown  in  Fig.  57,  so  that  the  hydrogen  may  be 

burned  as  it  escapes.  Do  not  apply  a 
light  till  you  have  made  sure  that  air  is 
all  driven  out  of  the  flask.  Why  ?  When 
the  hydrogen  is  burning,  notice  the  colour 
of  the  flame.  Hold  in  the  flame  a  porce- 
lain evaporating  dish  containing  water. 
Notice  whether  there  is  any  deposit  on  the 
dish.  If  there  is  not,  you  may  be  sure  tliat 
you  have  no  arsenic  in  the  materials  with 
which  the  hydrogen  is  prepared.  This  is 
a  very  important  precaution,  because  both 
zinc  and  sulphuric  acid  sometimes  contain  arsenic.  If 
there  is  no  deposit  on  the  dish,  introduce  through  the 
thistle-tube  a  few  drops  of  arsenic  dissolved  in  hydro- 
chloric acid.*  Does  the  flame  become  larger  or  smaller? 
What  is  its  colour  ?  Hold  in  it  a  porcelain  dish  as  before 
and  observe  the  character  of  the  deposit  formed  on  tlio 
dish.  It  should  be  of  a  grayisli  colour  and  look  like  a 
mirror.  This  is  called  Marsh's  test,  from  the  name  of  the 
man  who  first  used  it. 

In  the  case  of  ai'senic  poisoning,  the  arsenic  can  be  dis- 

*  Great  care  must  be  taken  not  to  allow  the  gas  to  escape  unbnrned 
Into  the  air,  and  ev  ;ii  the  fumes  produced  by  burning  it  should  not  be 
inhalec'.    It  is  advis.  ble  to  carry  on  the  operation  under  a  hood. 


s 

t 


Fio.  57 


THE  PHOSPHORUS   GROUP   OF  ELEMENTS         187 


mach  and 
poisoned 

lixture  of 
forms  an 

sual   way 
being  in 
n  may  be 
apply  a 
hat  air  is 
^?    When 
he  colour 
3  a  porce- 
ig  water, 
sit  on  the 
sure  that 
rials  with 
This  is 
ause  both 
;enic.      If 
ough  the 
in  hydro- 
smaller  ? 
as  before 
!d  on  tlio 
ok  like  a 
tne  of  the 

tn  be  dis- 

e  unbnrned 
)uld  not  be 
•d. 


solved  out  from  tlie  contents  of  the  stomach  and  the  solu- 
tion then  tested. 

The  compound  produced  in  Marsh's  test  for  arsenic  is 
hydrogen  arsenide  or  arseniuretted  hydrogen,  the  formula 
being  AsHg,  corresponding  to  Pllg.  It  cannot  be  made  in 
the  same  way  as  phosphoretted  hydrogen,  because  caustic 
soda  does  not  have  a  similar  action  on  arsenic  as  on  plios- 
phorus.  It  is  made  when  tlie  hydrogen  produced  by  tlie 
action  of  an  acid  on  zinc  acts  on  the  oxide  or  chloride  of 
arsenic. 

AsgOg  +  12 II  =  2  AsH^  +  3  l\f>. 

The  action  is  written  in  the  above  form  with  12  H  instead 
of  6  Ilg,  in  order  to  show  that  the  hydrogen  is  not  regarded 
as  formed  into  molecules  but  as  acting  on  the  arsenious 
anhydride  in  the  atomic  state. 

It  is  sometimes  said  that  tlie  hydrogen  is  nascent  or  in 
the  nascent  condition  —  that  is,  just  in  the  process  of  being 
formed  without  actually  being  separated.  The  term  is 
not  a  very  good  one,  because  the  outcome  is  the  result  of  a 
number  of  reactions  occurring  togetlier  in  tlie  solution,  and 
it  often  happens  that  a  process  producing  hydrogen  in  one 
way  causes  an  action  to  go  on  which  will  not  take  i)lace 
when  hydrogen  is  produced  in  another  way.  Practically 
all  that  is  meant  by  saying  that  the  action  is  due  to 
nascent  hydrogen  is  that  whe*  ydrogen  is  generated  and 
escapes  as  a  gas  it  does  not  \  ^c  in  the  same  way  as  when 
the  substance  to  be  acted  upon  is  mixed  with  the  materials 
which  would  naturally  produce  hvdrogen.  For  instance, 
in  the  above  case,  though  oxygen  would  be  taken  away 
from  arsenic  by  the  action  of  a  stream  of  heated  hy^'ogen, 
arseniuretted  hydrogen  would  not  be  produced,  perhaps 


188 


CHEMISTRY 


because  at  the  temperature  when  the  oxygen  would  be 
removed,  arseniuretted  hydrogen  would  be  decomposed. 

Arsenic  pentoxide,  AsgOg,  wliich  has  been  already  men- 
tioned, cannot  be  obtained  by  the  direct  union  of  arsenic 
and  oxygen,  as  arsenic  trioxide  may  be.  We  liave  seen  in 
several  cases  that  nitric  acid  oxidises  more  readily  than 
air  or  even  than  pure  oxygen,  and  by  the  action  of  nitric 
acid  on  arsenic  trioxide,  arsenic  acid  is  produced. 

The  equation  is  represented  by  the  eqtiation 


AsoOo  +  2  HNO„  +  2  H„0  =  2  H.AsO,  +  iV,0„ 


or 


arsenic  acid 


'2^3' 


AsnOo  -f  2  HNO«  +  2  H„0  =  2  H,AsO.  -\- JSfO  +  NO^, 


'2^3 


3' 


Arsenic  acid  is  in  many  respects  similar  to  phosphoric 
acid  HgPO^,  but  unlike  the  latter  all  the  water  can  be 
driven  off  from  it,  producing  AsgOg. 

Phosphoric  anhydride  is  made  by  the  direct  union  of 
oxygen  and  phosphorus,  and  when  united  with  water  can- 
not be  recovered.  Arsenic  anhydride  can  only  be  made 
by  first  preparing  its  compound  with  water  and  heating. 

Arsenic  acid  is  chiefly  used  in  calico  printing,  whereas 
arsenic  trioxide  is  employed  in  the  manufacture  of  some 
kinds  of  glass  and  in  making  some  colouring  matters  such 
as  Paris  green,  as  well  as  for  fly  and  rat  poisons.  Paris 
green  has  been  largely  replaced  as  a  colouring  matter  by 
non-poisonous  greens  and  is  chiefly  used  as  a  poison  for 
insects. 

Arsenic  is  found  native  to  some  extent,  also  as  sulphides, 
and  also  combined  with  metals.  Mispickel,  or  arsenical 
pyrites,  a  sulphide  of  arsenic  and  iron  (or  pyrites  in  which 
half  of  the  sulphur  is  replaced  by  arsenic),  whose  composi- 
tion is  represented  by  the  foi^nula  FeAsS,  is  the  most 


THE  PHOSPHORUS  GROUP  OF  ELEMENTS        189 


^ould  be 
posed, 
dy  men- 
'.  arsenic 
i  seen  in 
ily  than 
of  nitric 


0,, 

osphoric 
'  can  be 

anion  of 
iter  can- 
be  made 
eating, 
whereas 
of  some 
ers  such 
.  Paris 
atter  by 
)ison  for 

ilphides, 
irsenical 
n  which 
lomposi- 
le  most 


common  ore.  When  roasted  it  produces  arsenic  trioxide, 
which  can  be  reduced  by  heating  with  charcoal. 

Arsenic  is  metallic  in  lustre,  is  brittle,  has  a  specific 
gravity  5.7,  and  has  the  peculiarity  of  subliming,  tliat  is, 
of  going  off  in  vapour  without  melting.  Ice  below  the 
melting  point  gives  off  a  little  vapour,  iodine  below  its 
melting  point  gives  off  a  great  deal  of  vapour,  arsenic  can- 
not be  melted  under  ordinary  atmospheric  pressure,  but 
the  solid  is  converted  directly  into  vapour.  In  some  prop- 
erties arsenic  is  like  a  metal,  in  some  it  is  like  a  non- 
metal.  We  have  seen  that  there  are  similarities  between 
nitrogen  and  phosphorus  and  between  phosi)liorus  and 
arsenic.  There  are  the  compounds  NHg,  PHg,  and  Asllg, 
but  on  the  other  hand  arsenic  forms  alloys  with  metals. 
It  makes  the  alloys  hard  and  brittle  and  is  used  in  the 
manufacture  of  shot  in  order  to  produce  more  perfectly 
tlie  globular  form. 

Antimony.  —  Experiment  87.  Examine  a  piece  of  me- 
tallic antimony.  Is  it  malleable  or  brittle?  Look  at  the 
surface  or  the  edges,  and  see  if  it  shows  signs  of  bein[; 
crystalline.  Pure  antimony  has  very  distinct  crystals 
which  show  on  the  surface  in  the  fo^^m  of  a  star.  This  is 
frequently  used  as  a  test  of  the  purity  of  the  metal.  To 
a  small  piece  of  antimony,  add  strong  hydrochloric  acid. 
Does  the  metal  apparently  dissolve  ?  Heat.  Test  the 
liquid  with  sulphuretted  hydrogen.  I'o  another  piece  of 
antimony  add  strong  nitric  acid  in  the  same  way.  What 
effect  is  produced  on  the  metal?  Filter  off  some  of  the 
liquid,  evaporate  to  dryness,  and  see  whether  anything 
passed  into  solution. 

Antimony  forms  an  alloy  with  lead  which  is  used  as 
type  metal.     The  alloy  is  harder  than  pure  lead.     Anti- 


190 


CIIEMxSTnY 


mony  forms  a  coiiipouiid  v/ith  hydrogen,  similar  to  the 
compound  formed  by  phosphorus  and  arsenic.  Hydrogen 
antimonide  is  very  simihir  to  hydrogen  arsenide,  but  is 
still  more  easily  decomposed. 

Experiment  88.  Fit  up  an  apparatus  exactly  as  for 
Marsh's  test  for  arsenic  ;  but,  histead  of  adding  a  com- 
pound of  arsenic,  add  some  suitable  compound  of  anti- 
mony, such  as  tartar  emetic.  Notice  the  appearance  of 
the  flame.  The  colour  is  slightly  different  from  that  ob- 
tained on  the  addition  of  arsenic.  Examine  the  deposit 
made  on  a  cold  porcelain  evaporating  dish.  You  have 
now  seen  enough  to  show  you  that  the  chemist  must  be 
very  careful  to  distinguish  between  arsenic  and  antimony. 
In  cases  of  poisoning,  arsenic  is  suspected,  but  the  chemist 
must  always  make  sure  that  he  proves  the  presence  of 
arsenic,  and  not  antimony,  because  considerable  doses  of 
antimony  compounds  are  sometimes  used  in  medicine. 
There  is  a  little  difference  in  the  appearance  of  the  mirror 
produced  on  the  porcelain  dish  by  arsenic  and  antimony, 
and  other  tests  can  be  applied  to  it  which  decide  between 
them  conclusively. 

Antimony  is  found  in  nature  chiefly  as  stibnite,  a  com- 
pound with  sulphur,  whose  composition  is  given  by  the 
formula  SbgSg.  The  Latin  name  for  antimony  is  stibium^ 
whence  is  derived  the  name  stibnite.  It  is  a  black, 
crystalline  mineral,  but  an  orange-coloured  substance  of  the 
same  composition  is  obtained  by  the  action  of  sulphuretted 
hydrogen  on  a  solution  of  an  antimony  compound  The 
metal  has  a  specific  gravity  6.7,  and  melts  at  the  tempera- 
ture 450^  C.  Phosphorus,  arsenic,  and  antimony  have  a 
great  many  similarities  between  their  compounds,  and  they 
are,  in  some  respects,  like  nitrogen;  but  they  are  also  like 
bismuth. 


THE  PHOSPHOJiUS  GROUP  OF  ELEMENTS        191 


T  to  the 
lydrogen 
e,  but  is 

ly  as  for 
?  a  com- 

of  auti- 
irance  of 

that  ob- 
e  deposit 
fou  have 

must  be 
ntimony. 

chemist 
3sence  of 

doses  of 
medicine, 
le  mirror 
ntimony, 

between 

e,  a  com- 
Q  by  the 
3  stibium^ 
a  black, 
ice  of  the 
ihuretted 
id  The 
tempera- 
y  have  a 
and  they 
also  like 


Bismuth.  —  Bismuth  is  a  metal  a  good  deal  like  anti- 
mony, being  hard  and  brittle.  It  is  denser  than  antimony, 
just  as  antimony  is  denser  than  arsenic.  Its  specific  grav- 
ity is  9.8.  It  is  found  native,  and  also  as  a  sulphide, 
l^igSg.  It  forms  alloys,  some  of  which  are  very  easily 
melted  ;  one  called  Wood's  metal  fuses  even  in  boiling 
water. 

The  elements  nitrogen,  phosphorus,  arsenic,  antimony, 
and  bismuth  form  a  natvu'al  group,  that  is,  they  possess 
many  similarities  which  make  it  well  to  set  them  together. 
Some  of  these  similarities  are  such  as  to  be  taken  up  fully 
only  in  an  advanced  book  on  chemistry. 

There  are  differences  between  the  elements  that  are 
quite  as  interesting  as  their  similarities.  No  one  would 
think  of  calling  nitrogen  a  metal,  whereas  bismuth  has 
nearly  all  the  properties  of  a  metal.  Piiosphorus  is  also 
unlike  a  metal ;  antimony  in  many  respects  resembles  a 
metal ;  arsenic  is  midway  between.  The  higher  the 
atomic  weight,  the  more  metallic  properties  do  the  ele- 
ments of  this  group  possess. 

The  compounds  with  hydrogen  are  interesting.  Am- 
monia, NUg,  is  very  alkaline;  phosphine,  PHg,  is  not 
appreciably  alkaline,  but  can  be  made  to  produce  salts  by 
combining  with  some  acids  ;  arsine,  AsIIg,  is  more  readily 
decomposed  than  either  ammonia  or  pliosphine,  and  does 
not  form  salts,  nor  does  stibine,  SbHg.  Bismuth  does  not 
form  a  compound  with  hydrogen. 

The  oxygen  compounds  have  corresponding  similarities 
and  differences.  Some  of  the  compounds  of  nitrogen  and 
oxygen  have  neither  acid  nor  basic  properties.  Some  of 
them  form  acids,  but  none  form  bases.  Phosphorus  prob- 
ably has  no  oxides  except  those  which  form  acids.     The 


192 


CHEMISTRY 


oxides  of  arsenic  are  acid  in  character,  though  arsenic  tri- 
oxide  is,  in  some  respects,  like  a  base  ;  the  oxides  of  anti- 
mony are  basic  or  neutral  in  most  of  their  properties, 
though  some  of  them  act  feebly  as  acids  when  treated  with 
a  strong  alkali ;  while  the  oxides  of  bismuth  are  either 
neutral  or  basic. 

We  have  in  this  group,  then,  a  Tery  good  example  of 
how  difficult  it  is  to  draw  hard  and  fast  lines  in  nature. 
No  one  would  call  oxygen  and  nitrogen  metals  ;  every  one 
would  call  gold,  silver^  iron,  and  copper,  metals.  But 
when  we  come  to  elements  like  arsenic  and  antimony,  it  is 
difficult  to  say  which  to  call  them.  In  some  text-books  of 
chemistry  they  are  classed  as  metals,  in  others  they  are 
classed  as  non-metals.  So  with  the  distinction  between 
acid  and  base.  We  all  call  sulphuric  acid  an  acid,  and 
lime  a  base  ;  but  the  oxides  of  arsenic  and  antimony 
behave,  in  some  respects,  like  an  acid  oxide,  in  some 
respects  like  a  basic  oxide. 

Oxides  that  react  with  sulphuric  acid  to  produce  firm 
compounds,  we  reac'll}'  call  basic  ;  oxides  which  react  with 
caustic  potash  to  produce  firm  compounds,  we  readily  call 
acid ;  but  some  oxides  form  compounds,  though  not  very 
firm,  with  both  sulphuric  acid  and  caustic  soda,  and  so  the 
dividing  line  is  not  distinct.  The  change  of  properties  of 
the  elements  of  this  group  is  in  the  order  of  the  atomic 
weight,  as  may  be  seen  by  the  following  numbers  :  — 

N  =  14;  P  =  31;  As=75;  Sb  =  120  ;  Bi  =  207. 


senic  tri- 
1  of  anti- 
•operties, 
ited  with 
re  either 

ample  of 
1  nature, 
jvery  one 
lis.  But 
ony,  it  is 
-books  of 
they  are 

between 
acid,  and 
mtimony 

in   some 

luce  firm 
eact  with 
idily  call 
not  very 
[id  so  the 
Gerties  of 
e  atomic 


207. 


CHAPTER   XIV 


CARBON 


Preparation  of  Charcoal  in  the  Laboratory  and  Experi- 
ments with  it. — Experiment  89.  Fit  up  an  apparatus 
as  in  the  figure  (Fig.  58).  The  test-tube  a  at  the  left  has 
a  delivery-tube  which  passes  into  another  test-tube  5,  from 
which  there  is  a  delivery-tube  whose  end  dips  under  water 


in  a  trough  so  that  gases  may  be  collected.  Into  the  tube  a 
put  a  piece  of  wood,  and  heat.  What  bubbles  escape  at 
lirst  from  the  delivery-tube  in  the  trough  ?  Why  ?  Allow 
about  as  much  gas  to  escape  as  would  correspond  to  the 
volume   of   the  test-tubes  a  and  6,  and  then  collect  the 


o 


ion 


194 


CHEMISTRY 


gas  that  comes  over.  What  is  the  appearance  of  the  liquid 
which  first  distils  from  the  wood  and  collects  in  the  re- 
ceive Is  it  more  or  less  mobile  than  what  distils  at 
a  higher  temperature  ?  Does  more  gas  come  over  with 
the  earlier  portions  of  the  liquid  or  with  the  later  ? 
Why  does  it  take  longer  to  raise  the  temperature  of  wood 
than  to  raise  the  temperature  of  iron  ?  In  order  to 
answer  this  question,  consider  why  it  is  impossible  to 
heat  water  much  above  100°  C.  at  the  ordinary  atmospheric 
pressure.  Heat  the  tube  a  until  all  action  has  ceased. 
Test  some  of  the  gas  which  you  have  collected,  to  see 
whether  it  is  combustible  or  a  supporter  of  combustion. 
What  is  the  result  of  your  test  ?  Mix  other  portions  of 
the  gas  in  test-tubes  with  two,  four,  and  eight  times  the 
volume  of  air,  and  apply  a  light.  In  which  case  do  you 
get  the  greatest  explosion  ? 

Now  examine  the  liquid  contained  in  the  receiver  h. 
Notice  the  "  empyreumatic  "  smell.  Test  with  litmus.  Is 
it  acid,  alkaline,  or  neutral  ? 

As  you  have  seen  during  the  distillation,  the  liquid  con- 
sists of  different  constituents,  which  may  be  separated  from 
each  other,  though  the  operation  is  not  very  easily  per- 
formed and  is  hardly  suitable  for  you  to  attempt.  What 
do  you  see  in  place  of  the  wood  ?  How  does  the  volume 
compare  with  the  original  volume  ?  What  colour  has  the 
substance  ?  Is  it  more  or  less  easily  broken  than  the 
wood  from  which  it  was  made  ?  Does  it  take  fire  more  or 
less  easily  ?  What  did  you  find  about  the  combustibility 
of  the  gas  obtained  by  heating  the  wood  ?  What  reason 
is  there  for  the  difference  between  the  combustibility  of 
wood  and  the  charcoal  obtained  from  wood  ? 

Put  a  piece  of  the  charcoal  you  have  made,  or  another 


CAJiBOK 


195 


the  liquid 
n  the  re- 
distils at 
•ver  with 
le  later  ? 
!  of  wood 
order  to 
•ssible  to 
Qospheric 
s  ceased, 
d,  to  see 
iibustion. 
)rtions  of 
times  the 
e  do  you 

iceiver  b. 
;mus.     Is 

quid  con- 
ited  from 
isily  per- 
:.  What 
e  volume 
Lr  has  the 
thau  the 
3  more  or 
ustibility 
at  reason 
ibility  of 

r  another 


piece  of  wood  charcoal,  into  water.  Does  it  sink  or  float  ? 
Heat  to  redness  another  piece  of  cliarcoal,  holding  it  in 
the  flame  on  the  end  of  an  iron  wire  or  otherwise,  and 
then  dip  it  immediately  into  water.  Does  it  sink  or  float  ? 
If  charcoal  has  open  spaces  or  pores,  as  you  can  doubt- 
less see  it  has,  what  will  fill  them  when  the  charcoal 
is  allowed  to  cool  in  the  atmosphere  ?  Can  the  pores 
contain  more  air  when  the  charcoal  is  hot  or  when  it  is 
cold  ?  In  which  case  will  the  water  into  whicli  the  char- 
coal is  plunged  be  the  better  able  to  penetrate  tlie  pores 
of  the  charcoal  ?  What  reason  is  there  for  the  difl^'erent 
action  of  the  hot  and  cold  charcoal  when  plunged  into 
water  ?  Is  the  specific  gravity  of  charcoal  greater  or  less 
than  that  of  water?  Why  is  it  possible  for  Avood  and 
charcoal  to  become  water-logged  while  ice  cannot  be  water- 
logged ? 

Experiment  90.  Heat  a  piece  of  charcoal  as  before, 
and  introduce  it  while  hot  into  a  tube  containing  ammonia 
gas  over  mercury,  as  shown  in  the  figure  (Fig.  69). 
Notice  that  though  the  char- 
coal is  red  hot  before  dipping 
into  the  mercury,  it  may  be 
taken  in  the  fingers  immedi- 
ately after  it  is  under  the  sur- 
face of  the  liquid.  Why  is 
tiis  ?  Is  charcoal  a  good  or 
a  bad  conductor  of  heat  ?  In 
order  to  test  this,  hold  one  end  of  a  piece  of  charcoal  about 
an  inch  long  in  the  fingers,  and  put  the  other  end  in  a 
flame.  Try  a  piece  cf  iron  in  the  same  way.  Which  can 
you  the  more  easily  hold,  the  charcoal  or  the  iron  ?  Which 
is  the  better  conductor  of  heat  ?     What  bearing  has  this 


Fig.  59 


196 


CHEMISTRY 


experiment  upon  the  result  you  obtained  when  putting 
the  hot  cliarcoal  uncUn*  mercury  ?  Why  does  mercury 
rise  in  the  tube  iis  soon  us  the  charcoal  is  introduced  into 
the  ammonia  ?  Remove  the  cliarcoal,  and  once  more  intro- 
duce it  into  the  flame  of  your  burner.  What  difference 
is  there  between  the  appearance  of  the  flame  now  and 
when  the  cliarcoal  was  heated  in  it  before  ? 

Just  as  (charcoal  absorbs  ammonia,  it  also  takes  up 
impurities  from  the  air,  so  that  it  is  sometimes  used  for 
purifying  air  contaminated  by  sewer  gas  or  otherwise. 
Bone  charcoal  (or  bone  black),  obtained  by  the  distillation 
of  bones  in  the  same  way  as  wood  charcoal  is  obtained 
from  wood,  is  even  more  effective  than  wood  charcoal. 
Bone  black  contains  not  only  charcoal,  but  the  mineral 
matter  (chiefly  calcium  phosphate)  contained  in  bones. 
In  order  to  test  its  action,  shake  up  water  coloured  with 
indigo  or  litmus  with  a  quantity  of  bone  charcoal,  and 
filter.  How  does  the  colour  of  the  filtrate  compare  with 
that  of  the  liquid  before  treatment  with  charcoal  ? 

Charcoal  is  used  for  clarifying  sugar,  oils,  and  other 
liquids,  and  in  filters  for  purifying  drinking  water.  In 
all  cases  the  chai'coJ.  ultimately  becomes  clogged  with 
impurities  and  is  worse  than  useless  for  the  purpose  for 
which  it  is  employed.  It  may,  however,  be  renovated 
to  a  considerable  extent  by  exposure  to  the  air,  and  still 
better  by  reheating. 

Experiment  91.  Mix  together  powdered  charcoal  and 
powdered  cupric  oxide.  How  could  water  be  used  to 
separate  the  two  after  they  were  mixed  ?  Heat  some  of 
the  mixture  in  a  dry  test-tube,  or  better  in  a  closed  tube 
made  of  hard  glass.  What  is  there  in  cupric  oxide  with 
which  carbon  is  ready  to  combine  ?     What  would  be  left  ? 


CAliUON 


197 


putting 

mercury 

uced  into 

ore  intro- 

ilifference 

now  and 

takes  up 

used  for 

therwise. 

istillation 

obtained 

charcoal. 

)  mineral 

in  bones. 

ired  with 

■coal,  and 

pare  with 

1? 

and  other 
^ater.  In 
fged  with 
irpose  for 
renovated 
,  and  still 

ircoal  and 
3  used  to 
t  some  of 
osed  tube 
ixide  with 
d  be  left  ? 


What  is  its  colour?  How  could  you  separate  it  from  tiio 
excess  of  charcoal  ?  Examine  what  you  ol)tain  aft(!r  heat- 
ing, in  order  to  see  whether  your  results  corresjiond  to 
your  anticipations.  If  they  do  not,  take  pains  to  lind  out 
whether  your  work  was  faulty,  or  whether  your  anticipa- 
tions were  founded  on  wrong  ideas,  or  were  duo  to  in- 
correct reasoning. 

Production  of  Charcoal  on  the  Large  Scale.  —  Charcoal  is 
made  on  the  large  scale  in  this  country  chiefly  by  burning 
wood  in  "  charcoal  pits,"  as  shown  in  Fig.  60.     The  wood 


is  laid  in  piles  of  hemispherical  shape.  It  is  built  round 
a  central  opening  that  serve:i  as  a  chimney.  The  heap 
is  covered  with  earth,  with  a  few  draught  holes  at  the 
bottom.  In  this  way  only  a  small  quantity  of  air  can 
enter,  and  the  combustion  of  the  wood  is  incomplete.  All 
of  the  volatile  matters  like  those  which  you  collected,  are 
burned  and  thus  lost,  and  the  yield  of  charcoal  is  about 
20%  of  the  wood.*    Wood  is  more  economically  carbonised 

*  Instead  of  wood  being  built  in  a  heap  as  described,  and  covered  with 
earth,  it  i.s  sometimes  charnd  in  larj^e,  brick,  dume-shaped  enclosures. 


198 


CHEMISTRY 


in  retorts,  because  in  addition  to  the  other  products,  about 
30%  of  the  wood  is  obtained  as  charcoal.  One  form 
of  retort  is  shown  in  Fig.  61.     The  advantages  of  using 

the  retorts  is  not,  how- 
ever, so  great  as  might 
at  first  sight  appear,  be- 
cause there  is  the  ex- 
pense of  the  retorts  and 
fireplace,  and  of  the 
fuel  for  heating.  The 
gases  which  distil  from 
the  wood  may  be  used 
for  this  purpose,  leaving  the  liquid  part  of  the  distillate 
to  be  made  use  of  otherwise.  In  some  remote  places, 
where  wood  is  plentiful  and  the  expense  of  retorts  and 
other  parts  of  the  necessary  plant  would  be  large,  the  old 
method  of  "  charcoal  pits "  may  be  preferable  to  what 
appears  to  be  the  more  scientific  method  of  distillation. 
Lampblack  and  Other  Forms  of  Carbon.  —  Experiment 
92.  In  the  luminous  part  of  a  candle  or  gas  flame,  or  of 
an  oil-lamp  flame,  hold  a  piece  of  porcelain.  What  is  the 
nature  of  the  substance  deposited  on  the  porcelain?  It 
is  called  lampblack.  Lampblack  is  made  on  a  large  scale 
by  the  incomplete  combustion  of  substances  of  an  oily 
or  resinous  character,  such  as  crude  mineral  oils,  or  the 
knots  and  other  refuse  from  pitch-pine  and  hemlock. 
Figure  62  shows  how  the  operation  is  carried  out.  Lamp- 
black is  used  for  black  paint,  and  to  a  still  greater  extent 
for  printer's  ink. 

Charcoal  and  lampblack  are  two  forms  of  carbon,  and 
as  they  are  not  crystalline  they  are  called  amorphous. 
But  carbon  is  found  in  two  crystallised  forms,  one  of  them 


CARBON 


199 


lets,  about 
One  form 
5  of  using 
not,  h  ow- 
ns might 
ppear,  be- 
s  the  ex- 
etorts  and 
1  of  the 
ng.  The 
istil  from 
y  be  used 
distillate 
te  places, 
;torts  and 
!^e,  the  old 
to  what 
istillation. 

PERIMENT 

ame,  or  of 
hat  is  the 
Jlain?  It 
arge  scale 
)f  an  oily 
ils,  or  the 
hemlock. 
;.  Lamp- 
ter  extent 

rbon,  and 
norphous. 
le  of  them 


being  among  the  softest  of  minerals,  the  other  the  hardest 
mineral  known.  The  first  is  called  graphite,  from  the 
Greek  word  which  means  "to  write,"  the  other  is  the 
diamond.  Graphite  is  grayish  black  and  of  a  metallic 
lustre,  is  sometimes  called  black  lead^  and  is  used  in 
the  manufacture  of  the  so-called  lead-pencils,  —  the  very 
soft  lead  consisting 
chiefly  of  carbon, 
while  the  harder 
leads  are  mixed 
with  other  ingredi- 
ents. 

Graphite  is  very 
difficult  to  fuse,  and 
hence  is  used  in  the 
manufacture  of  cru- 
cibles, which  are 
vessels  such  as  that 
shown  in  Fig.  63, 
used  for  the  melt- 
ing of  ores  and  other 
materials.*  Graph- 
ite is  also  employed 
as  a  lubricant  to 
diminish  friction  be- 
tween rubbing  me- 
tallic surfaces.  It  is  likewise  used  as  a  protective 
covering  for  ironwork,  and  as  stove  polish.  Some  paints 
contain  a  large  aniuunt  of  graphite. 

*  The  name  crucible  is  said  to  have  been  given  to  these  vessels  be- 
cause the  old  alchemists  marked  them  with  the  sign  of  the  cross  in  order 
to  keep  away  the  influence  of  evil  spirits. 


Fia.  62 


200 


CHEMISTRY 


The  diamond  is  the  other  crystalline  form  of  carbon. 
Many  diamonds  are  coloured,  but  sometimes  they  are 
perfectly  clear  and  transparent.  The  coarser  varieties  of 
diamond  are,  because  of  their  hardness,  employed  in  drills 
for  boring  through  rocks.  Clear  diamonds  refract  and 
disperse  light  very  strongly,  and  therefore  make  very 
brilliant  gems,  having  a  peculiar  sparkle  and  flash.  This, 
with  the  hardness  of  the  diamond,  makes  it  the  most 
valuable    gem,   though   occasionally,   on   account   of   the 

fashion  prevailing  at  the 
time,  other  gems  may  bring 
a  higher  price.  When  the 
diamond  ^s  heated  in  ab- 
sence of  air,  it  swells  up 
and  forms  a  blacK  amor- 
phous mass.  Is  its  density 
thereby  increased  or  de- 
creased? 

What    is    formed    Avhen 

,  charcoal    burns    in    air    or 

I 

oxygen  ?  What  is  the  ac- 
tion of  the  product  upon 
lime-water  ?  Charcoal,  graphite,  and  diamond  differ  very 
much  in  appearance.  How  would  you  think  it  possible 
to  show  that  they  are  merely  different  forms  of  the  same 
element  ?  Lavoisier,  about  the  year  1775,  was  the  first  to 
prove  that  diamond  is  pure  carbon. 

It  is  easy  to  produce  graphite  or  amorphous  carbon 
from  any  other  form  of  carbon,  but  pure  brilliant  diamonds 
have  not  hitherto  been  made,  tliough  small  coloured  dia- 
monds have  been  produced  artificially.  Carbon  will  dis- 
solve in  molten   iron  just  as  salt  dissolves  in  water,  or 


r     limiji''      l!l|li''i|i^" 


H 


mr^ 


Fig.  63 


CABBON 


201 


)f  carbon. 

they  are 
arieties  of 
i  in  drills 
fract  and 
lake  very 
h.     This, 

the  most 
it  of  the 
at  the 
nay  bring 
^hen  the 
d  in  ab- 
svvells  up 
CK  amor- 
s  density 
I  or  de- 
ed when 
n  air  or 
:s  the  ac- 
uct  upon 
iffer  very 
b  possible 

the  same 
he  first  to 

IS  carbon 
diamonds 
>ured  dia- 
will  dis- 
water,  or 


sulphur  in  carbon  bisulphide,  and  if  there  is  a  good  deal 
of  carbon  dissolved  in  the  iron,  part  of  it  separates  as 
small  scales  of  graphite  when  the  iron  is  allowed  to 
cool  slowly.  Hydrochloric  acid  dissolves  iron,  but  not 
graphite.  Describe  how  you  would  separate  the  graphite 
from  the  iron. 

It  is  said  that  if  the  iron  is  under  great  j^'-sssure  the 
carbon  separates  in  the  diamond  form.  Possibly  this  is 
because  the  diamond  has  a  greater  specific  gravity  than 
graphite,  and  so  would  take  less  room,  but  we  know  too 
little  about  the  laws  of  crystallisation  to  make  any  certain 
statement. 

There  is  much  greater  difference  between  the  specific 
gravity  of  the  different  forms  of  carbon  than  between 
those  of  sulphur  or  ot  phosphorus.  The  specific  gravity 
of  diamond  is  3.3,  of  graphite  2.3,  and  of  some  forms 
of  charcoal  1.6. 

Coal.  —  You  have  learned  that  carbon  is  a  constituent 
of  wood.  It  also  forms  a  large  portion  of  coal.  Some 
coals  contain  little  else,  are  hard,  do  not  soil  th3  fingers, 
are  difficult  to  light,  and  burn  without  a  luminous  flame. 
Other  coals  are  softer,  soil  tlie  fingers,  are  much  more 
easily  kindled,  and  burn  with  a  luminous  flame.  The  first 
coal  is  often  called  anthracite,  the  other  bituminous  coal ; 
there  is  no  distinct  line  between  the  two  kinds.  Compare 
the  difference  between  the  flame  of  bituminous  coal  and 
anthracite  with  the  difference  between  the  flame  of  wood 
and  wood  charcoal.  What  reason  have  you  for  supposing 
that  anthracite  may  have  been  subjected  to  a  process  of 
destructive  distillation  ?  Does  ordinary  bituminous  coal 
liglit  more  or  less  readily  than  ordinary  wood?  When 
you  were  distilling  wood,  what  evidence  had  you  that 


202 


CHEMISTRY 


there  were  various  stages  in  the  process  of  distillation  ? 
What  reason  have  you  for  supposing  that  bituminous  coal 
may  have  been  subjected  to  a  process  similar  to  a  partial 
destructive  distillation  ? 

When  the  rocks  in  which  anthracite  is  found  are  ex- 
amined, they  show  evidence  of  having  been  subjected 
to  great  pressure  and  heat,  and  thus  it  seems  likely  that 
the  coal  itself  has  been  raised  to  a  high  temperature. 
From  a  microscopic  examination  of  ordinary  coal  it  appears 
to  be  formed  largely  from  parts  of  plants,  from  the  leaves 
and  seeds  and  spores  of  trees,  not  very  frequently  from 
the  woody  stems.  The  partial  distillation  does  not  need 
very  great  heat  if  time  is  allowed.  If  the  bottom  of  a 
little  pool  of  A\  ater  containing  a  quantity  of  dead  leaves 
and  plants  that  have  lain  a  long  time  be  stirred  up  with 
a  stick,  it  will  be  found  that  bubbles  of  gas  will  rise  to 
the  surface  of  the  water  and  may  be  lighted.  This  gas  is 
somewhat  similar  to  what  you  got  by  distilling  wood. 
The  process  of  decay  has  produced  something  similar  to 
the  process  of  distillation. 

Carbon  in  Organic  Tissue.  —  Not  only  do  wood  and  coal 
contain  carbon,  but  all  animal  and  vegetable  tissues,  so 
that  it  is  one  of  the  most  important  elements  in  nature. 
Plants  take  up  carbon  dioxide  from  the  air,  make  use  of 
the  carbon  and  some  of  the  oxygen  for  their  own  tissues, 
and  give  off  the  rest  of  the  oxygen  into  the  air  again. 
Animals  feed  upon  plants,  keep  some  of  the  carbon  for 
their  own  tissues,  and  exhale  some  of  it  as  carbon  dioxide, 
to  be  again  used  by  plants.  Since  carbon  dioxide  is 
produced  in  the  body  by  oxygen  of  the  air  uniting 
with  the  carbon  of  the  tissues,  we  have  an  instance  of  the 
slow   burning   of   carbon,  just  as   in  a  bog  we   have  an 


..'  » 


CARBON 


203 


tillation  ? 
nous  coal 
a  partial 

L  are  ex- 
subjected 
kely  that 
perature. 
it  appears 
he  leaves 
itly  from 
not  need 
torn  of  a 
ad  leaves 
i  up  with 
11  rise  to 
his  gas  is 
ng  wood, 
dmilar  to 

and  coal 
issues,  so 
n  nature. 
ke  use  of 
n  tissues, 
ir  again, 
irbon  for 
I  dioxide, 
ioxide  is 
:  uniting 
ce  of  the 

have  an 


example  of  slow  distillation.  When  wood  decays  in  the 
presence  of  air,  carbon  dioxide  is  produced,  and  in  this 
case  also  we  have  an  example  of  slow  combustion.  It  is 
worthy  of  note,  however,  that  this  slow  combustion  is  not 
known  to  go  on  except  in  living  tissues  or  under  the 
influence  of  living  organisms  (the  so-called  bacteria  uf 
decay). 

There  are  a  number  of  compounds  containing  carbon, 
so  many  that  the  study  of  them  forms  a  special  branch  of 
chemistry  called  organic  chemistry.  The  name  was  given 
because  the  compounds  were  at  one  time  considered  to  be 
the  product  of  life  and  to  be  incapable  of  formation  in  any 
other  way,  but  in  1828  a  sii  stance  which  had  hitherto 
been  obtained  only  from  animals  was  formed  artificially. 
Now,  not  only  are  many  animal  and  vegetable  products 
obtained  artificially,  but  many  so-called  organic  substances 
made  by  the  chemist  in  the  laboratory  are  not  produced 
by  any  living  organism.  Though  the  bulk  of  organic 
compounds  must  be  passed  over,  there  are  two  or  three 
compounds  of  carbon  and  hydrogen  which  it  will  be  well 
to  study. 

Methane.  —  What  is  the  formula  of  carbon  dioxide  ? 
How  many  atoms  of  oxygen  combine  with  one  atom  of 
carbon  ?  How  many  atoms  of  hydrogen  combine  with 
one  atom  of  oxygen  ?  How  many  atoms  of  hydrogen 
might  you,  therefore,  expect  to  combine  with  one  atom 
of  carbon  ?  Is  carbon  dioxide  a  solid,  a  liquid,  Oi  a  gas  ? 
In  which  of  the  three  states  might  we  expect  the  corre- 
sponding compound  of  carbon  and  hydrogen  to  exist  ? 

Preparation  of  Methane  and  Experiments  with  the  Gas.  — 
Experiment  93.  Mix  together  seven  or  eight  grammes 
of  dry  sodium  acetate  with  about  three  times  its  weight  of 


204 


CHEMISTRY 


soda  lime  (a  mixture  of  caustic  soda  and  quicklime)  and 
put  into  a  hard  glass  test-tube,  taking  care  that  the  test- 
tube  is  not  i-ore  than  half  full.  Lay  the  test-tube  on  its 
side,  and  tap  it  so  that  there  will  be  a  passage  along  the  top 
for  the  escape  of  gas.  Then  fit  up  as  in  the  figure  (Fig. 
64).  It  may  be  advisable  to  wrap  wire  gauze  round  the 
tube  in  order  to  make  the  heat,  which  is  afterward  to  be 

applied,  more  uni- 
form. Heat  the 
tube,  and  after  the 
air  has  been  driven 
out  collect  some 
of  the  gas  in  cylin- 
ders, but  before  it 
ceases  to  come  off, 
fit  the  exit  tube  to 
an  apparatus  such 
that  the  gas  may 
be  burned  in  a  jet. 
Apply  a  light  to 
the  gas.  What  is 
the  character  of  the  flame  ?  Is  it  luminous  or  non-lumi- 
nous ?  What  experiment  could  you  try  with  the  flame 
to  show  that  the  gas  contains  hydrogen  ?  Suppose  you 
invert  a  cylinder  containing  air  over  the  flame,  how  could 
you  prove  that  carbon  dioxide  is  produced  by  the  com- 
bustion ?  What  elements  do  you  now  know  to  exist  in 
the  gas? 

It  can  be  proved  that  the  composition  corresponds  to 
the  formula  CH^.  If  this  is  the  actual  formula,  how 
many  grammes  of  the  gas  would  go  into  22.253  litres? 
In  this  case  would  the  gas  be  heavier  or  lighter  than  air  ? 


Fig.  64 


CARBON 


205 


me)  and 
the  test- 
be  on  its 
g  the  top 
re  (Fig. 
ound  the 
ird  to  be 
lore  uni- 
[eat    the 
after  the 
3n  driven 
ct    some 
in  cylin- 
before  it 
come  off, 
t  tube  to 
btus  such 
gas  may 
I  in  a  jet. 
light   to 
What  is 
lon-lumi- 
:he  flame 
pose  you 
ow  could 
the  com- 
>  exist  in 

ponds  to 
ula,  how 
3  litres? 
ihan  air? 


In  order  to  see  whether  the  gas  is  in  reality  heavier  or 
lighter  than  air,  see  how  long  it  takes  for  i\  cylinder  or  a 
test-tube  full  of  the  gas  to  burn  when  the  vessel  is  turned 
mouth  upward  and  compare  with  the  time  required  to 
burn  the  gas  when  the  vessel  is  turned  mouth  downward. 
Introduce  into  a  cylinder  ten  volumes  of  air  with  one 
volume  of  the  gas  and  apply  a  light.  What  reason  liave 
you  for  considering  that  some  portion  of  the  air  combines 
with  great  energy  with  the  constituents  of  the  gas  ? 
Assuming  that  all  the  carbon  and  hydrogen  unite  with 
oxygen  of  the  air  in  the  above  case  and  that  tlie  above 
proportions  represent  the  proper  relative  amounts  of  air 
and  gas,  how  many  volumes  of  pure  oxygen  would  be 
required  for  the  complete  combustion  of  the  gas  ?  Which 
of  the  two  following  equations  would  represent  the 
action  ? 

Does  the  formula  which  you  decided  upon  from  the 
density  of  the  gas  correspond  with  that  required  by  the 
volume  of  air  needed  for  its  complete  combustion,  or 
does  it  differ  ?     What  is  the  formula  so  derived  ? 

The  gas  is  methane,  popularly  called  mar  ii  gas,  because 
found  in  marshes,  as  already  described. 

Its  formation  by  the  action  of  soda  lime  on  sodium 
acetate  may  be  represented  by  the  equation 

NaCaHgOa  +  NaOH  =  NagCOg  +  CH^, 

How  many  litres  of  methane  can  be  prepared  from  eight 
grammes  of  sodium  acetate  ? 

It  will  be  seen  that  the  equation  does  not  take  any 


206 


CHEMISTRY 


account  of  the  lime  in  tlie  mixture.  The  reaction  would 
go  on  with  caustic  soda  alone  without  the  presence  of 
lime,  but  the  latter  prevents  the  mass  irom  fusing  too 
readily  and  attacking  the  glass. 

How  much  of  the  carbon  in  sodium  acetate  is  obtained 
as  methane  ?  From  what  does  the  hydrogen  of  the  me- 
thane come  ?  What  reason  is  there  for  considering  that 
the  formula  CHgCOgNa  shows  the  nature  of  sodium 
acetate  better  than  the  formula  NaCgHgOg  ? 

The  reaction  which  goes  on  may  be  represented  by 
writing  the  equation  in  the  following  form  : 


CH3 
+     H 


COgNa 
ONa 


Cff^  +  NaaCOg. 


When  formulae  are  written  in  a  manner  intended  to 
show  their  chemical  relationships,  they  are  called  struc- 
tural formuhe.  The  formula  for  sodium  acetate  in  the 
last  equation  shows  the  relationship  supposed  to  exist 
between  the  two  carbon  atoms,  one  of  them  being  united 
with  all  of  the  hydrogen,  the  other  with  all  of  the  oxygen, 
though  no  particular  effort  is  made  to  show  the  relation- 
ship existing  between  the  latter  carbon  atom  and  the 
oxygen  and  sodium  most  closely  connected  with  it. 

Methane  is  a  gas  of  specific  gravity,  0.55,  it  is  very 
slightly  soluble  in  water,  and  is  difficult  to  liquefy,  requir- 
ing to  be  cooled  to  —  164°  C.  at  atmospheric  pressure. 

In  some  coal  mines  it  is  found  to  a  very  considerable 
extent  and  forms  a  great  danger  because  of  the  readiness 
with  which  a  mixture  with  air  will  explode,  a  little  more 
than  5%  of  methane  being  all  that  is  required.  It  is 
called  "  fire-damp  "  by  the  miners,  and  mines  in  which  it 
is  found  are  said  to  be  "fiery."     The  explosion  produces 


CARBON 


207 


m  would 
sence  of 
sing  too 

obtained 

the  me- 

•ing  that 

sodium 

mted  by 


ended  to 

ed  struc- 

e  in  the 

to  exist 

ig  united 

3  oxygen, 

relation- 

and  the 

it. 

t  is  very 
Yt  requir- 
isure. 
isiderable 
readiness 
ttle  more 
d.  It  is 
which  it 
produces 


carbon  dioxide,  wliich  is  very  suffocating  and  is  the  "choke- 
damp  "  of  the  miners.  This  forms  an  additional  danger, 
because  even  if  the  direct  effect  of  the  exi)l()si(m  be 
escaped,  fatal  results  are  liable  to  result  from  the  inhaling 
of  choke  damp. 

Acetylene 

Preparation  of  Acetylene  and  Experiments  with  the  Gas. 

—  ExPEUiMENT  1)4.  Introduce,  as  in  Fig.  65,  a  small 
piece  of  calcium  carbide  (the  size  of  a  small  bean)  into 
a  cylinder  full  of 
water  inverted  over 
a  pneumatic  trough. 
It  is  not  a  very 
good  plan  to  intro- 
duce it  with  the  fin- 
gers. The  student 
should  now  be  able 
to  devise  the  most 
suitable  method  by 
wliich  he  may  carry 

out  the  operation.  What  is  the  effect  of  tlie  water  upon 
the  calcium  carbide  ?  When  the  gas  ceases  to  be  evolved, 
invert  the  cylinder,  having  put  a  cover-glass  over  the 
mouth  in  the  usual  manner  ;  and  when  it  is  right  side  up, 
remove  the  cover-glass  and  apply  a  light.  How  does  the 
flame  of  the  gas  compare  with  that  of  methane  ?  Is  it 
more  or  less  luminous  ?  Is  the  flame  of  methane  or  of 
this  gas  more  like  that  of  hydrogen  ? 

The  gas  is  acetylene. 

Mix  one  volume  of  the  gas  with  between  twelve  and 
thirteen  volumes  of   air,  and  apply  a  light.     What  are 


Fig,  {\o 


208 


CHEMISTRY 


you  to  infer  from  the  fact  that  an  explosion  takes  place  ? 
How  does  it  compare  with  the  explosion  of  marsh  gas? 
Be  careful  in  trying  this  experiment.  Tt  is  well  to  wrap 
a  towel  round  the  cylinder. 

If  possible,  arrange  some  apparatus  by  which  it  will  be 
possible  to  burn  the  gas  at  a  jet.  If  you  have  a  gas 
holder  of  the  ordinary  kind,  it  will  be  easy  enough ;  if 
not,  a  bottle  provided  with  a  cork  and  tubes,  as  in  the  fig- 
ure (Fig.  QG^^  may 
be  used.  The  tube 
at  which  the  gas  is 
to  be  burned  has  a 
very  fine  opening, 
smaller  than  is  usu- 
ally employed  for  the 
burning  of  gases;  the 
other  tube,  part  of 
which  is  rubber,  is 
connected  with  a  res- 
ervoir of  water.  As 
water  flows  in,  the 
acetylene  with  which 
the  bottle  has  been 
filled,  and  which  must  have  no  air  mixed  with  it,  flows 
out  as  a  jet  and  may  be  burned.  The  flow  of  water  is 
regulated  by  a  pinch-cock.  Figure  67  shows  a  simple 
contrivance  by  which  the  gas  may  be  generated  as  re- 
quired, and  exhibits  a  special  form  of  burner. 

Hold  a  dry  porcelain  dish  just  above  the  visible  flame 
and  see  if  you  can  obtain  evidence  of  the  existence  of 
hydrogen  in  acetylene.  Afterwards  put  the  porcelain  into 
the  luminous  part  of  the  flame  and  see  if  you  can  obtain 


Fig.  66 


CARBON 


209 


es  place  ? 
irsh  gas? 
1  to  wrap 

it  will  be 

ve  a  gas 

lough ;   if 

n  the  fig- 

56),   may 

The  tube 

le  gas    is 

d   has   a 

open  ng, 

n  is  usu- 

ed  for  the 

^ases;  the 

part   of 

•ubber,   is 

i^ith  a  res- 

ater.     As 

3    in,   the 

ith  which 

has   been 

it,  flows 

water  is 

a  simple 

ed  as  re- 

ble  flame 
stence  of 
elain  into 
m  obtain 


evidence  of  the  existence  of  carbon  in  the  gas.  What  is 
the  evidence  in  each  case?  How  does  the  luminosity  of 
the  acetylene  flame 
compare  with  a  candle 
flame  of  the  same  size  ? 
How  does  the  colour  of 
the  flames  compare  ?  * 
Acetylene  has  only 
lately  boen  made  in 
large  quantity,  because 
it  is  only  lately  that 
calcium  carbide  has 
been  manufactured 
upon  the  large  scale. 
The  carbide  is  pre- 
pared by  heating  a 
mixture  of  powdered 
coke  and  quicklime  in 
an  electric  furnace. f  - 
Except  at  this  high 
temperature      oxygen 

cannot  be  removed  from  lime  by  means  of  carbon,  but 
in  the  electric  furnace  the  reaction  goes  on. 

CaO  +  3C  =  CaC2+  00. 

When  calcium  carbide  is  put  into  water  the  calcium  once 

*  The  acetylene  flame  is  liable  to  smoke,  but  will  not  do  so  if  the  open- 
ing at  which  it  burns  is  fine  enough  and  the  flow  of  gas  is  not  too  rapid. 
It  is  best  to  have  a  very  fine  opening  so  that  considerable  pressure  may 
be  put  upon  the  gas.  Special  forms  of  burner  are  manufactured  for  the 
\'se  of  acetylene  as  an  illuminant. 

t  Coke  is  the  rfslHup  left  by  the  destructive  distillation  of  coal,  and 
consists  mainly  of  carbon. 


Fivi.  G7 


210 


CHEMISTRY 


more  unites  with  oxygen,  leaving  hydrogen  for  the  carbon. 
Why  would  you  not  expect  to  find  quicklime  produced 
in  the  reaction?  What  actually  does  happen  is  repre- 
sented by  the  equation 

CaCo  +  2  H„0  =  CaOoHn  -f  C^E^. 


2"2 


'2"2' 


What  is  the  difference  in  composition  between  the  sub- 
stance represented  by  the  formula  CaOgHg  and  quicklime  ? 

If  CjHg  is  the  formula  for  acetylene,  how  must  its  den- 
sity compare  with  that  of  air?  How  could  you  decide  by 
experiment  whether  this  is  approximately  its  density?* 
Assuming  that  C2^^2  ^'^  ^^^^  formula,  make  an  equation  rep- 
resenting complete  combustion  of  the  gas  with  oxygen. 
What  volume  of  oxygen  is  required  for  the  complete 
combustion  of  one  litre  of  acetylene?  What  volume  of 
carbon  dioxide  would  be  produced?  How  does  the  result 
of  your  calculation  agree  with  what  you  were  told  about 
the  quantity  of  air  you  were  to  mix  with  acetylene  in 
order  to  obtain  an  explosive  mixture? 

The  li^ht  of  the  acetylene  flame  is  more  like  dt.ylight 
than  that  provided  by  any  other  known  illuminant,  and 
hence  colours  have  the  same  shade  when  illuminated  by 
acetylene  as  when  viewed  by  the  light  of  the  sun.  As  the 
flame  is  very  brilliant,  acetylene  is  being  introduced  some- 
what as  an  illuminant  instead  of  ordinary  gas  or  the 
electric  light. 

Acetylene  can  be  liquefied  by  a  pressure  of  sixty-three 
atmospheres  at  10°  C,  and  it  is  sometimes  sold  in  the 
liquid  state  in  strong  iron  cylinders  ;  but  there  have  been 

*  Your  experiment  could  not  decide  between  the  formula  C2H2  and 
C2H8.  Tliat  is  arrived  at  by  gravimetric  analysis.  Tlie  density  experi- 
ment would  decide  between  the  formulae  CH,  C2H2,  C4H4,  etc. 


CAR HON 


211 


le  carbon, 
produced 
is  repre- 


the  sub- 
uicklime  ? 
its  den- 
decide  by 
density  ?  * 
ation  rep- 
li  oxygen. 

complete 

volume  of 

the  result 

:old  about 

etylene  in 

e  di.ylight 
inant,  and 
linated  by 
1.  As  the 
iced  some- 
:as  or  the 

ixty-three 
)ld  in  the 
have  been 

la  C2H2  and 
nsity  experi- 
c. 


a  number  of  explosions  with  liquid  acetylene,  and  its  use 
has  therefore  been  limited.  If  it  were  not  for  this  ten- 
dency to  explode,  the  liquid  miglit  l)e  used  for  prodr  '  g 
gas,  as  it  occupies  a  small  bulk,  and  a  cylinder  01  e 
liquid  would  supply  light  for  a  long  time. 

Ethylene  is  another  important  compound  of  hydrogen 
and  carbon.  Its  fornuda  is  C2II4.  At  one  time  methane 
was  known  as  light  carburetted  hydrogen  and  ethylene  as 
heavy  carburetted  hydrogen.  It  will  be  seen  from  the 
formula  that  for  the  same  amount  of  hydrogen  there  is 
twice  as  much  carbon  in  ethylene  as  in  methane.  It  is 
more  dense ;  it  is  more  easily  liquefied,  being  liquefied  at 
0*^  C.  under  a  pressure  of  forty -one  atmospheres  and  at 
—  103°  C.  under  ordinary  atmospheric  pressure.  It  can 
be  made  by  the  action  of  sulphuric  acid  on  alcohol.  The 
acid  abstracts  the  elements  of  water,  so  that  the  reaction 
may  be  represented  as  simply  a  decomposition  of  alcohol 
into  ethylene  and  water. 

alcohol  ethylene 

Figure  68  shows  an  apparatus  that  may  be  used,  but 
the  operation  is  somewhat  difficult.  Ethylene,  as  might 
naturally  be  supposed  from  the  quantity  of  carbon  in  it, 
burns  with  a  luminous  flame,  being  intermediate  in  this 
respect  between  methane  and  acetylene.  Ethylene  is  an 
important  part  of  the  ordinary  gas  used  for  illuminating 
purposes. 

Hydrocarbons  —  Bonds.  —  We  have  now  considered  three 
gases  which  are  compounds  of  hydrogen  and  carbon.  A 
large  number  of  substances  are  compounds  of  these  two 
elements  and  are  called  hydrocarhom.     When  there  is  a 


212 


CHEMISTRY 


I- 


considerable  number  of  atoms  of  carbon  in  the  molecule, 
the  hydrocarbon  is  liquid ;  when  there  is  a  still  larger 
number  of  carbon  atoms  in  the  molecule,  the  hydrocarbon 
is  solid.  You  have  had  an  illustration  of  this  tendency 
in  the  compounds  studied.  Methane  needs  a  very  low 
temperature  for  its  condensation,  acetylene  can  be  con- 
densed at  ordinary  temperature  by  sufficient  pressure,  and 
ethylene  is  still  more  easily  condensed. 


V==7 


Fio.  68 


In  methane  it  is  seen  that  one  atom  of  carbon  combines 
with  four  atoms  of  hydrogen,  and  carbon  is  therefore  seen 
to  be  quadrivalent.  We  have  had  to  deal  with  the  com- 
pounds HCl,  HjO,  NHg,  and  CH^,  and  we  call  chlorine  a 


CARBON 


213 


molecule, 
still  larger 
>^drocarbon 
3  tendency 
I  very  low 
m  be  con- 
essure,  and 


univalent  element,  oxygen  a  bivalent,  nitrogen  a  triva- 
lent,  and  carbon  a  quadrivalent.*  We  do  not  know  what 
physical  condition  is  the  basis  of  this  difference  between 
the  elements.  It  may  possibly  be  due  to  a  difference  of 
shape  in  the  atoms,  but  we  have  no  evidence  upon  the 
point.  We  sometimes  speak  of  the  atoms  as  though 
they  were  united  by  bonds,  we  say  that  chlorine  has  one 
bond,  oxygen  two,  nitrogen  three,  and  carbon  four,  and 
we  represent  the  above  formulae  in  the  following  way : 

H 


n  combines 

refore  seen 

;h  the  com- 

chlorine  a 


H  -  CI,        H  -  O  -  H,        H  -  N  -  H, 


M 


II_C  -H. 

I 


These  formulae  are  not  intended  to  represent  the  position 

of   the   atoms   in  space.      Ns— H   would   represent   the 

formula  of  ammonia  as  well  as  that  given  above.  The 
giving  of  these  formulae  does  not  necessarily  imply  that 
the  atoms  really  have  bonds,  but  their  action  may  be  rep- 
resented as  though  they  had  bonds,  just  as  we  speak  of 
a  current  of  electricity,  although  we  have  no  idea  as  to 
what  electricity  actually  is. 

In  the  compound  CgH^  it  might  perhaps  seem  that 
carbon  is  not  quadrivalent,  but  it  is  evident  that  ''^  we  are 
to  represent  two  atoms  of  carbon  as  existing  in  combina- 
tion in  a  molecule,  it  is  as  reasonable  to  represent  them  as 
united  to  each  other  by  bonds  as  to  represent  them  as 

*  Monovalent  and  tetravalent  are  sometimes  used  instead  of  univalent 
and  quadrivalent,  but  they  are  mongrel  words,  derived  from  both  Greek 
and  Latin,  and  therefore  not  so  good. 


214 


mEMISTRY 


united  by  bonds  to  atoms  of  other  elements.  There  is  a 
hydrocarbon  with  which  we  have  not  experimented  whose 
composition  is  represented  by  the  formula  CgHg.     This 

H     H 

II 
formula  is  often  written  H  —  C  —  C  —  H,  where  it  will  be 

II 
H      H 

seen  that  each  carbon  atom  has  four  bonds.  In  the  same 
way  ethylene  CgH^  may  be  represented  by  the  formula 


I 

C 


( 


=  ( 


I 


and  acetylene  by  C  =  C 

I        I 
H     II. 


Flame.  —  The  gases  methane,  ethylene,  and  acetylene 
are  constituents  of  most  flames  used  for  illuminaUiig  pur- 
poses, and  this  is  a  suitable  place  for  considering  flames  in 
general.  Flames  always  consist  of  a  combination  of  gases, 
and  all  the  ordinary  illuminating  flames  consist  of  a  com- 
bination of  gases  with  the  oxygen  of  the  air.  In  the 
ordinary  gas  flame  this  is  at  once  evident.  In  the  case  of 
lamps,  the  oil  which  is  drawn  up  into  the  wick  is  volatil- 
ised, with  more  or  less  decomposition,  and  the  gis  so 
produced  is  what  burns ;  in  the  candle  the  wax  is  first 
melted  and  afterward  volatilised.  Compare  the  com- 
bustion of  charcoal  and  wood.  In  which  case  is  there 
a  flame?  Is  c^^'rcoal  an  easy  or  a  difficult  substance  to 
volatilise  ?  Though,  however,  burning  gases  produce  a 
flame,  the  flame  may  not  be  luminous.  Is  the  flame  of 
hydrogen  luminous?  of  carbon  monoxide?  of  acetylene? 
of  alcohol  ?  of  methane  ?    Into  a  non-luminous  flame  intro- 


CARBON 


215 


here  is  a 
fced  whose 
Hg.     This 


it  will  be 


the  same 
e  formula 


acetylene 
ating  pur- 
i;  flames  in 
n  of  gases, 

of  a  com- 
In  the 
:-he  case  of 
is  volatil- 
lie  gas  so 
[IX  is  first 
the  com- 
3  is  there 
3stance  to 
produce  a 
3  flame  of 
tcetylene  ? 
ime  intro- 


duce  a  fine  platinum  wire  or  shake  some  powdered  char- 
coal. Which  gives  the  greater  light,  the  burning  gas  or 
the  solid  introduced  into  the  flame  ? 

Experiment  95.  Examine  the  flame  of  a  candle.* 
Place  a  piece  of  porcelain  in  the  luminous  part  of  the 
flame.  What  evidence  is  there  that  carbon 
exists  in  the  solid  condition  in  it  ?  At  the 
first  glance  it  will  seem  that  the  flame  con- 
sists of  two  parts,  —  a  briglit  yellow  or  lumi- 
nous portion  and  a  bluish  or  non-luminous 
portion.  Examine  the  flame  closely.  Notice 
that  there  is  a  part  of  the  flame  near  its  base 
of  a  deeper  blue  tint  than  the  rest.  Move 
the  candle  rapidly  tlirough  the  air  so  tliat 
there  is  little  of  the  luminous  flame.  Does 
the  deep  blue  part  become  more  or  less  dis- 
tinct? Do  you  consider  that  the  blue  is 
more  or  less  hot  than  the  luminous  portion  ? 
Look  to  see  whether  you  can  detect  any  flame  outside  the 
luminous  part.  If  not,  shake  a  dusty  cloth  beside  the 
flame  and  see  the  effect,  or  bring  a  splinter  of  wood  almost 
to  the  edge  of  the  lower  part  of  the  luminous  flame. 
Figure  69  represents  a  candle  flame  with  its  different  parts 
differently  shaded. 

Bring  down  over  the  flame,  so  as  almost  to  touch  the 

wick,  a  piece  of  stiff  white  paper. 
Remove  the  paper  before  it  catches 
fire,  but  not  before  it  is  partly 
charred.  Which  part  of  the  flame 
chars  the  paper  more,  the  middle 
or   the   outside  ?     See    if    your   result   corresponds  with 

*  A  tallow  candle  with  a  big  flame  is  best  for  these  experiments. 


Fig.  ()•> 


Fia.  70 


216 


CHEMISTRY 


Fig.  70.  Hold  across  the  flame  a  piece  of  wood,  such  as 
a  match,  until  it  begins  to  burn.  Blow  out  the  flame  of 
the  match  at  once,  and  examine  the  wood.  There  should 
be  an  uncharred  portion  between  two  charred  parts. 
Remembering  that  the  combustion  is  a  combination  of 
gases  from  the  candle  with  oxygen  of  the  air,  why  would 

you  not  expect  the  space 
immediately  surrounding 
the  wick  to  be  very  hot  ? 
A  candle  flame  is  usu- 
ally described  as  hollow, 
the  interior  consisting 
merely  of  gas  produced 
by  a  volatilisation  of  the 
melted  wax  of  the  candle. 
Introduce  rapidly  into 
the  middle  of  the  flame 
the  head  of  a  match  and 
notice  that  it  does  not  ignite  for  some  time.  If  you  have 
an  alcohol  lamp,  make  a  large  flame  and 
introduce  into  it  a  small  quantity  of  gun- 
powder, on  the  point  of  a  knife-blade  or 
other  piece  of  metal.  It  should  not  catch 
fire.  Another  method  of  carrying  out  the 
experiment  is  shown  in  Fig.  71.  Put  a 
small  heap  of  gunpowder  upon  a  shallow 
plate  or  in  an  evaporating  dish,  pour  a  lit- 
tle alcohol  over  it  and  light  the  alcohol. 
Inside  the  burning  alcohol,  the  gunpowder 
remains  unaffected  until  the  alcohol  is 
nearly  all  burned  off  so  that  the  outside  of  the  flame 
cames  in  contact  with  the  gunpowder,  or  until  the  flame  is 


Fig.  71 


Fia.  72 


)d,  such  as 
e  flame  of 
ere  should 
red  parts, 
•illation  of 
vhy  would 

the  space 
irrounding 

very  hot  ? 
me  is  usu- 
as  hollow, 
consisting 

produced 
ion  of  the 
he  candle. 
>idly    into 

the  flame 
natch  and 
:  you  have 


CARBON 


217 


ria.  72 

the  flame 
le  flame  is 


blown  to  one  side  by  a  draught  of  air,  which  may  produce 
the  same  effect.  With  a  tube  of  rather  fine  bore  you  may 
find  it  possible  to  draw  off  the  gases  from  the  interior  of 
the  flame  of  the  candle  and  to  ignite  them  at  the  farther 
end  of  the  tube  in  the  manner  shown  by  Fig.  72. 

To   illustrate   the   effect   of    cooling   a   flame   try   the 
following: 

Experiment  96.  Bring  down  upon  the  flame  a  sheet 
of  metal,  as  in  Fig.  73.  How  does  it  affect  the  luminosity 
of  the  flame?  What  reason 
does  this  experiment  give  you 
for  supposing  that  the  luminous 
part  of  the  flame  is  hotter  than 
the  blue  portions  ?  See  whether 
the  candle  can  be  put  out  by 
contact  with  the  piece  of  metal. 

Make  a  close  spiral  of  half  a 
dozen  turns  of  fine  copper  wire 
by  wrapping  it  round  a  small 
lead  pencil  or  glass  tube,  and 
bring  it  down  over  the  flame  so 
that  it  will  surround  the  wick, 
as  in  Fig.  74.  Notice  the  change 
in  luminosity  of  the  flame  be- 
fore it  goes  out.  The  extin- 
guishing of  the  flame  is  due  to 
the  gas  being  cooled  below  its  kindling  point  by  tlie  copper 
Hold  a  wire  gauze  over  the  flame,  bringing  it  down 


Fig.  73 


wire. 


slowly  so  as  not  to  extinguish  the  flame.  Does  the  flame 
pass  through  the  gauze?  Does  the  gas  from  the  candle  pass 
througli  the  gauze  ?  If  it  does,  it  should  be  possible  to  light 
it  on  the  upper  side  of  the  gauze.     Make  t^.o  experiment. 


218 


CHEMISTRY 


Fig.  75 


If  you  have  any  kind  of  gas  flame,  it  will  be  easier  to 
perform  the  experiments  with  wire  gauze.     Turn  on  the 

gas  jet  with- 
out lighting 
the  gas.  Hold 
a  piece  of 
gauze  about 
an  inch  or 
so  above  the 
jet,  as  shown 

in  Fig.  75,  apply  a  light  above 
the  gauze,  and  notice  whether 
the  gas  lights  below  the  gauze. 
Sir  Humphry  Davy,  about  a 
century  ago,  made  use  of  the 
facts  which  you  have  noticed 
in  order  to  provide  protec- 
tion for  miners  in 
fier}^  mines.  His 
invention  c  o  n- 
sists  in  surround- 
ing a  lamp  with 
^^^-  ^^  wire    gauze    and 

thus  preventing  the  flame  setting  fire  to  the 
explosive  mixture  outside.  Air  can  of  course 
pass  through  the  gauze,  so  that  the  lamp  may 
be  kept  burning ;  but  though  the  fire-damp 
may  be  seen  burning  inside  the  gauze,  the  gas 
outside  does  not  take  fire,  at  least  for  some 
time,  so  that  the  miner  has  an  opportunity  to  Fig.  76 
leave  the  dangerous  locality.  If  the  gas  burns  a  long 
time  inside  the  gauze,  the  latter  may  become  hot  and  bO 


B  easier  to 
rn  on  the 


Fig.  75 

ight  above 
;e  whether 
the  gauze. 
^,  about  a 
use  of  the 
VQ  noticed 
ie  protec- 


CARBON 


219 


Fig.  7G 


a  long 


ot  and 


bO 


set  fire  to  the  gas  outside;  hence  Davy's  "  safety  lamp"  is 

useful  chiefly  for  giving  warning  to  tlie  miner  in  time  to 

enable  him  to   avoid   the   danger.      Figure   76  shows  a 

Davy's  safety  lamp. 

Experiment  97.    If  you  have  a  supply  of  gas  in  the 

laboratory,  make  use  of  a  Bunsen  burner,  named  from  its 

inventor,  perhaps  the  most 

famous  chemist  of  the  nine- 
teenth century.     Figure  77 

represents  a  Bunsen  burner. 

Notice  that  the  opening  of 

the  tube  A  from  which  the 

gas  comes  out  is  wide,  in 

this  respect  quite  different 

from  the   ordinary  gas  jet. 

Unscrew  the  upright   tube 

and  notice  that  the  opening 

through  which  the  gas  issues 

into  it  is  small.     A  Bunsen 

burner  thus  divided  is  rep- 
resented in  Fig.  78,  the 
opening  being 
a.     Notice  that 

there  are  two  wide  openings  at  the  bottom  of 
the  upright  tube.  The  burner  is  usually  pro- 
vided with  a  metal  ring  by  which  the  open- 
ings may  be  closed.  Close  these  openings, 
turn  on  the  gas,  and  light  it  as  it  escapes. 
Can  you  see  the  parts  of  the  flame  noticed 
in  the  candle  ?  Gradually  turn  the  ring  so  as 
to  open  the  holes  slowly.     What  is  the  effect 

on  the  luminosity  of  the  flame  ?     Does  the  exterior  non- 


L 


Fig.  77 


Fig.  78 


220 


CHEMISTRY 


luminous  flame  become  more  or  less  distinct  ?  Can  you 
still  detect  the  four  parts  of  the  flame  ?  Note  the  variations 
in  them  as  the  ring  is  turned.  Whac  do  you  observe  about 
the  size  of  the  flame  as  a  whole  ?  Place  a  piece  of  smoking 
paper  near  the  lower  openings.  What  evidence  have  you 
that  air  is  drawn  in  through  these  openings  ?  When  the 
luminous  part  of  the  flame  is  just  disappearing,  what  is 
the  colour  of  the  inner  cone  ?  What  has  taken  the  place  of 
the  luminous  part  of  the  flame  ?  Open  the  air  draught  as 
much  as  possible  and  the  inner  cone  will  probably  become 
green ;  if  not,  turn  off  the  gas  a  little.  Decrease  the 
supply  of  gas  still  more.  You  will  probably  find  that  the 
flame  disappears  from  the  top  of  the  long  tube  and  that 
the  gas  lights  below.  The  flame  is  then  said  to  "  strike 
hack.''^  If  it  is  allowed  to  remain  in  this  condition  for  a 
minute  or  two,  you  will  notice  a  very  disagreeable  smell 
due  to  acetylene,  produced  when  gas  burns  with  an  insuf- 
ficient supply  of  air. 

In  the  ordinary  non-luminous  flame  of  the  Bunsen 
burner,  when  the  inner  cone  has  a  bluish  shade,  the  ratio 
of  gas  to  air  in  the  mixture  which  reaches  the  top  of  the 
tube  is  about  1  :  2.3 ;  when  the  colour  is  green,  the  ratio 
of  gas  to  air  is  about  1  :  3.4.  Suppose  that  the  gas 
requires  as  much  oxygen  as  would  be  needed  for  complete 
combustion,  if  it  consisted  of  50%  methane  and  50%  of 
a  gas  which  needs  no  oxygen,  calculate  how  much  air 
would  be  required  and  see  if  the  ratios  given  above  would 
be  enough.  The  striking  back  is  caused  by  an  explosive 
mixture  of  air  and  gas  being  produced.  A  little  considera- 
tion will  make  it  plain  that  this  explosive  mixture  contains 
the  greatest  proportion  of  gas  to  air  which  can  explode 
through  the  tube.     So  long  as  the  gas  is  in  a  greater  ratio, 


CARBON 


221 


Can  you 
variations 
erve  about 
f  smoking 
I  have  you 
When  the 
g,  what  is 
le  place  of 
Iraught  as 
ly  become 
3rease  the 
d  that  the 
and  that 
to  "  strike 
tion  for  a 
ible  smell 
an  insuf- 

e  Bunsen 
,  the  ratio 
-op  of  the 
,  the  ratio 
t  the  gas 
•  complete 
d  50%  of 

much  air 
3ve  would 

explosive 
considera- 
e  contains 
n  explode 
iater  ratio, 


its  mixture  with  air  burns  quietly  at  the  top  of  the  burner; 
but  finally  enough  air  mixes  with  the  amount  of  gas  sup- 
plied to  cause  a  rapid  ignition  through  the  tube,  the  flame 
travelling  back  more  quickly  than  the  gas  and  air  flow  out. 

Test  which  is  the  hottest  part  of  the  flame  by  seeing 
where  a  fine  platinum  wire  placed  in  it  becomes  brightest. 
You  should  find  the  highest  temperature  at  approximately 
the  middle  of  the  outer  cone.  Try  experiments  similar  to 
those  carried  out  with  the  candle  to  show  the  hollow  nature 
of  the  ordinary  non-luminous  flame. 

It  is  possible  to  arrange  a  Bunsen  flame  so  that  the 
inner  and  outer  cone  can  be  separated.  Over  the  ordinary 
metal  tube  of  the  burner  fit  a  glass  tube  about  ten  or 
twelve  inches  long,  and  outside  this  fit  another  glass  tube 
of  a  little  wider  bore  and  arranged  so  that  it  may  be 
moved  up  and  down.  A  good  way  is  to  have  between 
the  two  glass  tubes  one  or  two  rubber  rings  (which  may 
be  made  by  cutting  off  half  an  incli  or  so  of  rubber  tubing 
large  enough  to  go  over  the  inner  glass  tube).  The 
arrangement  is  shown  in  the  figure  (Fig.  79).  In  the 
first  instance  let  the  outer  tube  project  three  or  four 
inches  above  the  inner  tube  and  light  the  gas  as  it 
escapes.  Diminish  the  supply  of  gas  so  that  the  propor- 
tion of  air  becomes  greater  till  the  inner  cone  finally 
becomes  green.  Diminish  still  further  the  supply  of  gas, 
and  the  inner  cone  will  strike  down  and  burn,  leaving 
the  outer  cone  burning  at  the  top  of  the  outer  tube. 

Modify  the  experiment  so  that  the  inner  tube  will  pro- 
ject beyond  the  outer,  as  in  Fig  80,  and  liglit  the  gas. 
The  double  cone  will  now  be  seen  at  the  top  of  the  inner 
tube.  Move  the  outer  tube  upwards,  and  it  will  carry 
with  it  the  outer  cone,  leaving  the  inner  cone  burning  at 


222 


CHEMISTRY 


the  top  of  the  inner  tube.  There  is  a  possibility  of  the 
hot  flame  cracking  the  ghiss,  so  you  will  And  it  advisable 
to  insert  in  the  tup  of  each  glass  tube  a  small  piece  of 
platinum  foil  in  such  a  way  as  to  form  a  short  platinum 


See 


tube  projecting  about  a  centimetre  above  the  glass, 
whether  the  upper  or  the  lower  flame  is  the  hotter  by 
passing  a  platinum  wire  down  through  them  and  seeing 
where  it  is  brightest. 

There  has  of  late  been  a  very  extensive  study  of  flames ; 
the  temperature  of  the  different  parts  has  been  carefully 


CARBON 


2li3 


ity  of  the 
t  advisable 
11  piece  of 
platinum 


investigated,  and  the  gases  in  different  parts  of  the  flame 
have  been  analysed.  In  the  ordinary  luminous  llame 
there  is  the  outer  envelope,  which  is  not  easily  scun,  but 
in  which  the  greater  part  of  the  combustion  really  takes 
place  and  which  is  the  hottest  part  of  the  flame.  The 
inner  portion  is  partly  non-luminous  and  partly  luminous. 
In  the  non-luminous  portion  there  is  very  little  air  and 
therefore  a  minimum  of  combustion  ;  the  gases  are,  how- 
ever, lieated  and  undergo  change,  tlie  most  important 
apparently  being  that  some  acetylene  is  produced.  But 
acetylene  when  sufficiently  lieated  decomposes,  and  by 
its  very  decomposition  produces  heat,  for  it  is  one  of 
those  substances  which  are  formed  oidy  under  the  con- 
tinuous influence  of  heat,  and  it  therefore  gives  out  heat 
when  it  decomposes.*  Hence  the  carbon  produced  by  the 
decomposition  is  at  a  high  temperature  and  becomes  lumi- 
nous. The  carbon  takes  oxygen  from  carbon  dioxide  and 
water  vapour,  which  are  produced  in  the  outer  envelope 
of  the  flame  and  which  penetrate  to  some  extent  into  the 
inner  portion  of  the  flame.  Carbon  monoxide  and  hydro- 
gen are  thus  produced,  and  these  are  consumed  in  the 
outer  non-luminous  envelope.  The  deep  blue  part  of  the 
flame  near  its  base  is  probably  similar  to  the  luminous 


lass.  See 
hotter  by 
nd  seeing 

of  flames ; 
carefully 


*  Hydrogen  and  oxygen,  when  they  combine  to  form  water,  give  out 
heat,  and  if  water  is  to  be  decomposed  it  requires  the  application  of  heat 
or  some  other  form  of  energy.  Water  is  said  to  be  exothprmie^  because 
giving  out  heat  in  its  formation.  On  the  other  ham),  carbon  and  liydro- 
gen  do  not  readily  combine  to  form  acetylene,  and  some  other  operation 
by  which  heat  is  afforded  must  go  on  at  tlie  same  time.  In  the  case  of 
the  action  of  calcium  carbide  on  water,  the  union  of  calcium,  hydrogen 
and  oxygen  to  form  calcium  hydroxide  produces  a  great  amount  of  heat 
and  helps  the  union  of  carbon  and  hydrogen.  Acetylene  is  said  to  be 
endothermic,  because  absorbing  heat  in  its  formation. 


224 


CHEMISTRY 


I  fl 


part,  except  tliat  tlie  tempeniture  is  not  liigli  enough  to 
cause  a  decomposition  of  the  hydrocarbons  into  carbon 
and  hydrogen. 

The  amount  of  air  drawn  in  by  the  Hunsen  burner  is 
not  sufficient  for  the  complete  combustion  of  the  gas,  and 
a  hotter  flame  may  be  made  by  forcing  air  into  the  middle 
of  the  flame.  This  is  done  in  the  blast  lamp,  which  con- 
sists essentially  of  two  tubes, 
an  inner  and  an  outer  one,  as 
shown  at  d  in  Fig.  81.  The 
inner  tube  supplies  air,  while 
gas  is  supplied  through  the 
passage  between  the  tubes.  The 
air  is  forced  in  through  the  tube, 
and  so  into  the  interior  of  the 
flame,  by  means  of  bellows  or 
some  similar  contrivance  con- 
nected with  the  tube  c.  The 
supply  of  air  being  large,  tlie 
^1  combustion  of  the  gas  is  rapid 
and  the  temperature  high.  The 
blast  is  used  in  the  laboratory  when  a  high  temperature 
is  required.  If  oxygen  be  used  instead  of  air,  the  tem- 
perature is  still  higher,  because  the  nitrogen  of  the  air 
does  not  support  combustion  and  has  to  be  heated. 
Hydrogen  gives  a  higher  temperature  than  ordinary  illu- 
minating gas,  and  the  flame  of  a  blast  lamp  in  Avhich 
oxygen  and  hydrogen  are  employed,  and  which  is  usually 
,  called  the  oxyhydrogen  blowpipe,  is  the  hottest  that  we 
can  produce.  Platinum,  which  is  very  difficult  to  melt, 
fuses  readily  in  the  oxyhydrogen  flame,  which  is  therefore 
used  in  the  working  of  that  metal. 


Fig.  81 


CARBON 


225 


enough  to 
nto  carbon 

n  burner  is 
lie  gas,  and 
the  middle 
which  con- 
two  tubes, 
ter  one,  as 
.  81.     The 

air,  wliile 
irough  the 
tubes.  The 
^h  the  tube, 
rior  of  the 
bellows  or 
vance  con- 
)e   c.     The 

large,  tlie 
as  is  rapid 
high.  The 
Dmperature 
r,  the  tem- 

of  the  air 
be  heated, 
iinary  illu- 
3  in  w^hich 
I  is  usually 
ist  that  we 
lit  to  melt, 
s  therefore 


The  flame  is  non-luminous,  but  a  solid  which  will  not 
melt  when  put  into  it  becomes  white  hot  and  emits-  light. 
Such  a  substance  is  quicklime,  and  one  of  the  most  brill- 
iant liglits  known  is  produced  by  the  oxyhydrogen  ihmie 
striking  upon  a  piece  of  quicklime.  This  is  what  is  ordi- 
narily called  the  lime  light.  (Figure  82  shows  the  appa- 
ratus.) Since  the  extensive  application  of  electricity,  the 
oxyhydrogen  flame  is  not  so  important  as  it  formerly  was. 


Fig.  82 


Instead  of  a  blast  from  a  bellows,  air  is  sometimes  sup- 
plied to  a  small  flame  by  means  of  a  mouth  blowpipe. 
The  outer  portion  of  this  flame  contains  a  quantity  of 
heated  oxygen  and  may  be  used  in  order  to  oxidise  sub- 
stances. For  instance,  a  small  piece  of  metallic  arsenic 
placed  on  a  stick  of  charcoal  and  heated  in  the  outer 
flame  is  oxidised  and  gives  arsenic  trioxide.  On  the 
other  hand,  the  interior  of  the  flame  has  not  sufficient 
oxygen  for  complete  combustion  of  the  gas,  and  so  it 
would  take  oxygen  from  substances  ready  to  give  it. 
For  example,  if  copper  oxide  on  a  stick  of  charcoal  is 
submitted  to  the  action  of  the  inner  part  of  the  flame, 
oxygen  is  taken  away  and  copper  is  left  in  the  metallic 
state.     The  outer  portion  of  the  flame  is  called  the  oxi- 


226 


CHEMISTRY 


ipiiil 


dising  flame,  the  inner  the  reducing  flame.     The  appear- 
ance of  the  blowpipe  and  the  method  of  use  is  shown  in 

the  figure  (Fig.  83). 
The  mouth  blowpipe 
is  very  much  used  for 
the  identification  of 
metals  in  ores,  owing 
to  the  fact  that  the 
compounds  of  many 
metals  give  character- 
istic reactions  when 
heated  in  the  oxidising 
or  reducing  flames. 

Silicon  and  Boron. 
—  There  are  two  ele- 
ments, silicon  and  bo- 
ron, which  are  in  many  respects  like  carbon.  The  com- 
pound of  silicon  and  oxygen,  silica,  is  very  common, 
quartz  being  more  or  less  pure  silica,  and  many  rocks, 
such  as  granite,  containing  a  large  percentage  of  the  same 
substance.  The  compounds  of  boron  are  far  less  abun- 
dant, and  neither  boron  nor  silicon  has  the  same  interest 
as  carbon. 


mmiiii, uuuuiiiiiam"' 


Pig.  83 


riie  appear- 
is  shown  in 

(Fig.  88). 
h  blowpipe 
ch  used  for 
ification  of 
ores,  owing 
:3t  that  the 
J  of  many 
e  character- 
tions  when 
he  oxidising 
^  flames. 
and  Boron. 
ire  two  ele- 
con  and  bo- 

The  com- 
y  common, 
nany  rocks, 
of  the  same 

less  abun- 
,me  interest 


CHAPTER  XV 


METALS 


The  elements  that  we  have  so  far  studied  have,  for  the 
most  part,  belonged  to  the  class  called  non-metals.  We 
saw  in  the  group  containing  phosphorus,  arsenic,  antimony, 
and  bismuth,  that  the  line  of  division  between  non-metals 
and  metals  is  not  sharp ;  but  it  is  usually  convenient  to 
make  such  a  division.  The  non-metals  which  ccmi])ine 
with  oxygen  form  oxides  that  yield  acids,  and  these  acids 
may  have  their  hydrogen  replaced  by  a  number  of  ele- 
ments to  form  salts.  Several  of  the  non-metallic  elements 
form  acids  simply  by  combining  with  hydrogen.  Perhaps 
the  metallic,  or  non-metallic,  property  of  an  element  may 
be  considered  as  most  clearly  shown  by  the  nature  of  the 
chlorides.  The  chlorides  of  nearly  all  tlie  non-metallic 
elements  are  decomposable  by  water.  Very  few  of  the 
non-metallic  chlorides  have  been  studied  by  us,  for  the 
very  reason  that  they  are  not  important  and  are  easily 
decomposed.  The  chlorides  of  phosphorus  (of  which  there 
are  two,  PCI3  and  PClg)  are  decomposed  by  water,  and 
form  acids.  The  chloride  of  arsenic,  ASCI3,  also  decom- 
poses in  water  and  forms  the  oxide  (arsenic  trioxide), 
unless  in  the  presence  of  a  large  excess  of  hydrochloric 
acid.  The  chlorides  of  antimony  and  bismuth  are  par- 
tially decomposed  by  water,  forming  comi)()unds  which 
contain  some  chlorine  and  some  oxygen.     But  zinc  chlo- 

227 


228 


CHEMISTRY 


ride,  magnesium  cliloride,  calcium  chloride,  potassium  chlo- 
ride, and  sodium  chloride  have  no  tendency  to  decompose. 
The  action  of  nitric  acid  is  also,  in  many  cases,  an  indica- 
tion of  the  metallic,  or  non-metallic,  character  of  an  ele- 
ment. Nitric  acid  acting  on  phosphorus,  arsenic,  or 
antimony  merely  oxidises  it,  and  does  not  form  a  nitrate  ; 
with  bismuth  a  nitrate  is  produced  which  is,  however, 
partially  decomposable  by  water.  Nitric  acid  also  merely 
oxidises  sulphur  and  carbon,  but  silver  nitrate,  cupric 
nitrate,  cobalt  nitrate,  are  stable  salts. 

Salts  contain  a  metal  and  a  salt  radical,  and  if  the  salt 
radical  has  the  opportunity  to  choose  between  two  metals, 
it,  in  some  cases,  shows  its  preference  in  a  very  marked 
manner. 

Experiment  98.  Into  a  solution  of  copper  sulphate 
put  some  nails,  or  other  bright  pieces  of  iron.  What  evi- 
dence do  you  at  once  have  that  copper  is  removed  from 
the  solution  ?  Test  a  dilute  solution  of  copper  sulphate 
by  adding  potassium  ferrocyanide  solution.  What  appear- 
ance do  you  notice  ?  Into  some  more  of  the  dilute  solu- 
tion put  a  number  of  bright  iron  pieces,  suci  as  a  number 
of  tacks,  and  leave  them  until  the  colour  of  the  copper 
sulphate  disappears  from  the  solution.  Then  add  potassium 
ferrocyanide  again.  What  kind  of  precipitate  do  you  now 
obtain?  Dissolve  some  iron  in  sulphuric  acid  and  add 
potassium  ferrocyanide.  What  kind  of  precipitate  do 
you  obtain?  What  do  you  infer  was  in  the  solution 
from  which  the  copper  had  been  removed  by  the  iron? 
Dissolve  some  arsenic  trioxide  in  hydrochloric  acid,  and 
put  into  the  solution  a  strip  of  bright  copper  foil.  What 
happens  to  the  surface  of  the  copper  ?  Try  the  same  ex- 
periment with  copper  in  a  solution  of  mercuric  chloride. 


METALS 


229 


slum  chlo- 
ecompose. 
an  indica- 
of  an  ele- 
irsenic,  or 
a  nitrate  ; 
,  however, 
Iso  merely 
ite,  cupric 

if  the  salt 
wo  metals, 
ry  marked 

r  sulphate 
What  evi- 
oved  from 
sr  sulphate 
lat  appear- 
Lilute  solu- 
5  a  number 
the  copper 
.  potassium 
lo  you  now 
I  and  add 
ipitate  do 
e  solution 
the  iron? 
?  acid,  and 
)il.  What 
le  same  ex- 
c  chloride. 


What  do  you  infer  from  the  appearance  of  the  copper  in 
each  case  ? 

Experiment  99.  Into  a  copper  sulphate  solution 
pour  some  caustic  soda  solution.  What  is  the  colour  of 
the  precipitate  ?  Heat  the  precipitate  in  the  liquid.  What 
change  is  there  in  the  former  ?  Filter  off  and  test  some 
of  the  filtrate  by  adding  hydrochloric  acid  and  barium 
chloride.  What  have  you  proved  to  exist  in  the  solution  ? 
The  reaction  on  addition  of  the  caustic  soda  is  represented 
by  the  equation 

CuSO^  +  2  NaOH  =  Cu  (0H)2  +  NaaSO^, 
and  the  reaction  on  heating  is  represented  by 

Cu(0H)2  =  CuO  +  HgO. 

Examine  a  solution  of  ferric  chloride.  What  colour  is  it  ? 
Add  caustic  potash  solution  till  the  liquid  is  alkaline  to 
litmus.  What  is  the  appearance  of  the  precipitate  ?  It 
has  much  the  same  composition  as  rust.  Boil  the  liquid 
together  with  the  precipitate.  Does  the  latter  api)arently 
change,  as  in  the  case  of  the  precipitate  obtained  from  the 
copper  ?  Filter,  and  into  some  of  the  filtrate  put  enough 
hydrochloric  acid  to  neutralise  or  make  slightly  acid,  and 
then  add  potassium  ferrocyanide.  Is  there  any  i'-on  in  the 
solution  ?  How  would  you  test  for  iron  in  the  precipitate  ? 
Evaporate  some  more  of  the  filtrate  to  dryness  and  test 
for  potassium  and  for  a  chloride. 

The  reaction  which  takes  place  is  represented  by  the 
equation 

FeClg  +  3  KOH  =  Fe  (OH).,  4-  3  KCl. 

ferric  ferric 

chloride  hydroxide 


230 


(JIIEMISTRY 


The  term  ''hydroxide,"  or  "hydrate,"  is  applied  to  combi- 
nations of  metals  with  the  radical  OH.  The  hydroxides 
are  derivatives  of  water,  one-half  of  the  hydrogen  being 
replaced  by  the  metal.  A  univalent  metal  replacing  half 
the  hydrogen  in  one  molecule  of  water  forms  one  molecule 
of  an  hydroxide.  Thus  one  molecule  of  potassium  hydrox- 
ide (or  caustic  potash),  KOH,  or  of  sodium  hydroxide, 
NaOH,  is  deiived  from  one  molecule  of  water,  HOH. 
On  the  other  hand,  in  the  formation  of  one  molecule  of 
cupric  hydroxide,  Cu(0H)2,  two  molecules  of  water  are 
required,  copper  in  the  cpric  compounds  being  bivalent. 
In  the  case  of  ferric  hydroxide  one  molecule,  Fe(OH)3,  is 
derived  from  three  molecules  of  water.  The  formula  of 
the  hydroxide  may  be  written  if  the  formula  of  the  chlo- 
ride is  known,  because  for  every  chlorine  atom  in  the  mole- 
cule of  the  chloride  there  exists  an  OH  group  (often  called 
hydroxyl)  in  the  hydroxide.  Thus,  as  CaClg,  MgClg, 
PbClg,  represent  the  molecules  of  the  chlorides  of  calcium, 
magnesium,  and  lead,  so  Ca(0H)2,  Mg(OH).^,  Pb(0H)2, 
represent  the  molecules  of  the  hydroxides  of  the  same 
metals.  Sodium  and  potassium  have  a  greater  affinity  for 
the  radical  SO^  and  the  element  chlorine  than  has  either 
copper  or  iron.  We  found  that  iron  has  a  stronger  affin- 
ity for  the  radical  SO^  than  copper  has,  and  if  a  strip  of 
iron  and  a  strip  of  copper  be  put  into  a  dilute  solution  of 
sulphuric  acid,  and  joined  by  a  wire  outside  the  liquid,  a 
current  of  electricity  will  flow  from  iron  to  copper  in  the 
liquid,  and  the  ircn  is  said  to  be  electropositive  toward 
copper.  Sodium  and  potassium  are  electropositive  toward 
nearly  all  other  metals,  and  many  metals  may  be  obtained 
from  their  salts  by  the  action  of  sodium  and  potassium ; 
and  though  sodium  and  potassium  as  ordinarily  seen  do 


METALS 


231 


to  combi- 
lydroxides 
gen  being 
acing  naif 
3  molecule 
m  bydrox- 
lydroxide, 
er,  HOH. 
lolecule  01 
water  are 

bivalent. 
kOH) 


3' 


IS 


brmula  of 
the  chlo- 
1  the  mole- 
"ten  called 
V  MgCl^, 
•f  calcium, 
Pb(0H)2, 
the  same 
iffinity  for 
has  either 
iiger  affin- 
a  strip  of 
olution  of 
5  liquid,  a 
per  in  the 
/e  toward 
ve  toward 
!  obtained 
otassium ; 
y  seen  do 


not  appear  metallic,  the  reason  is  that  tliLy  are  so  ready 
to  combine  with  oxygen  that  the  metallic  lustre  is  seldom 
seen.  You  have  already  learned  (page  I'i)  bow  to  ob- 
tain a  brightly  metallic  surface. 

Metals  are,  for  the  most  part,  heavy,  but  lithium  is  the 
lightest  solid  known,  and  there  are  several  metals  lighter 
than  water.  Most  of  the  metals  melt  only  at  a  high  tem- 
perature, but  mercury  is  liquid  much  below  the  ordinary 
temperature,  freeziug  only  at  about  —  40°  C. 

Most  of  the  metals  are  of  a  white  or  grayish  colour,  but 
copper  is  red,  while  calcium,  strontium,  and  gold  are  yel- 
low. JNIetals  are  for  the  most  part  good  conductors  of 
electricit},  though  the  variation  in  this  respect  is  consid- 
erable. 

The  combinations  which  metals  make  with  each  other 
differ  from  those  which  they  make  with  non-metals.  In 
the  first  place,  they  combine,  in  most  cases,  in  all  propor- 
tions, and  moreover  the  combinations  are  rather  mixtures 
than  compounds,  being  something  like  solutions,  though 
alloys  are  sometimes  obtained  in  crystals  in  which  the 
elements  are  in  atomic  proportions.  Alloys  do  not  lose 
their  metallic  appearance,  and  their  properties  are  more 
nearly  a  mean  of  the  properties  of  the  constituents  than 
is  the  case  with  more  decided  chemical  compounds. 

In  the  chemical  study  of  metals  the  combinations  with 
non-metals  are  most  important,  and  we  found  it  impossi- 
ble to  study  the  non-metals  without  at  the  same  time 
learning  some  of  the  prr,perties  of  metals. 


CHAPTER  XVI 


THE  ALKALI  METALS 


Sodium.  —  One  of  the  most  common  substances  is  com- 
mon salt.  You  have  already  learned  that  it  is  composed 
of  sodium  and  chlorine.  Nearly  all  of  the  compounds  of 
sodium  are  made  by  taking  it  as  the  starting  point.  The 
largest  chemical  industry  is  connected  with  the  treatment 
of  common  salt  for  the  products  to  be  obtained  from  it, 
so  much  so  that  the  name  "  chemical  works  "  is  applied  to 
works  in  which  salt  is  one  of  the  raw  materials. 

Salt  is  obtained  from  sea-water,  from  rock  salt,  and 
from  salt  brines  derived  from  springs,  lakes,  or  wells.  In 
hot  countries  salt  is  obtained  from  sea-water  by  evapora- 
tion ;  in  cold  countries  the  salt  solution  is  concentrated 
by  freezing,  because,  as  you  saw  at  the  very  beginning 
of  your  work,  ice  formed  from  salt  water  contains  very 
little  salt,  and  hence  the  solution  left  behind  contains  a 
larger  proportion  of  salt  than  the  original  sea-water. 

Rock  salt  is  occasionally  found  pure  enough  for  use, 
grinding  only  being  necessary ;  more  frequently  it  must 
be  purified.  Brines  from  salt  wells  contain  a  larger  pro- 
portion of  salt  than  sea-water,  and  hence  do  not  need  so 
much  fuel  for  evaporation. 

From  common  salt  by  the  action  of  strong  sulphuric 
acid,  sodium  sulphate  is  made,  hydrochloric  acid  being 
produced  at  the  same  time.     The  operation  is  carried  on 

232 


THE  ALKALI  METALS 


233 


es  IS  corn- 
composed 
pounds  of 
Mnt.  The 
treatment 
i  from  it, 
applied  to 

salt,  and 
wells.  In 
Y  evapora- 
icentrated 
beginning 
tains  very 
contains  a 
ater. 

1  for  use, 
y  it  must 
irger  pro- 
t  need  so 

sulphuric 
cid  being 
arried  on 


in  large  furnaces,  in  one  form  of  which  the  floor  is  cir- 
cular and  rotates;  the  mixed  sodium  chloride  and  sul- 
phuric acid  are  introduced  in  a  continuous  stream  to  the 
middle  of  the  rotating  "  hearth,"  and  are  gradually  worked 
by  mechanical  scrapers  towards  the  edge.  By  this  time 
the  hydrochloric  acid  has  been  all  driven  off,  and  the 
sodium  sulphate  is  ready  to  be  removed  from  the  liearth. 
The  sulphate  is  called  "  saltcake,"  and  is  mainly  used  for 
the  manufacture  of  soda.  Some  is,  however,  employed  in 
glass  making,  in  the  production  of  ultramarine,  and  to 
some  extent  in  medicine. 

When  sodium  sulphate  is  dissolved  in  water  and  allowed 
to  crystallise  by  evaporating  the  solution  at  the  ordinary 
temperature,  the  crystals  have  the  composition  repre- 
sented by  the  formula  NagSO^,  10  HgO,  and  constitute 
"  Glauber's  salts,"  the  form  used  in  medicine. 

When  this  crystallised  sodium  sulphate  is  dissolved  in 
water,  it  is  found  that  the  solubility  increases  with  the 
temperature  up  to  about  33°  C,  after  wliich  it  decreases. 
It  is  also  found  that  if  a  solution  is  evaporated  between 
the  temperatures  33°  C.  and  40°  C,  the  sulphate  deposited 
contains  no  water  of  crystallisation.  Hence  the  solubility 
below  33°  C.  is  the  solubility  of  the  hydrated  salt,  Na2S()4, 
10  HgO;  Avhile  the  solubility  above  33°  C.  is  the  solubility 
of  the  anhydious  salt,  NagSO^.  The  solubility  of  anhy- 
drous sodium  sulphate  decreases  with  rise  of  temperature, 
and  thus  the  increase  of  solubility  followed  by  the  decrease 
is  accounted  for. 

Experiment  100.  —  Mix  in  a  beaker  powdered  crys- 
talline sodium  sulphate,  NugSO^,  10  HgO,  with  strong 
hydrochloric  acid,  both  being  at  the  temperatiiro  of  the 
laboratory.     What  evidence  does  the  outside  of  the  beaker 


23i 


CHEMISTRY 


i 


in  a  short  time  give  that  the  mixture  is  cohl?  In  the 
liquid  formed,  allow  a  test-tube  containing  water  to  re- 
main for  some  time.  What  happens  to  the  water  ?  Test 
the  temperature  with  a  thermometer.  What  temperature 
do  you  find  ?  Sodium  chloride,  which  is  formed  in  the 
reaction,  does  not  contain  water  of  crystallisation.  What 
becomes  of  the  water  ?  What  effect  does  that  have  upon 
the  temperature  ? 

By  far  the  greatest  quantity  of  sodium  sulphate  made 
is  used  in  the  manufacture  of  sodium  carbonate  in  "  soda  " 
works.  TI.ie  process  employed  was  invented  by  Le  Blanc, 
who  won  the  prize  offered  by  the  French  Academy  for 
the  best  method  of  preparation  of  sodium  carbonate  from 
common  salt.  Le  Blanc's  process  was  patented  in  1791, 
but  in  the  French  Revolution  his  property  was  seized  and 
he  committed  suicide.  The  process  has  been  but  slightly 
changed  to  the  present  day.  Sodium  chloride  cannot  be 
changed  into  carbonate  by  the  action  of  carbonic  acid, 
because  the  latter  is  a  weak  acid,  and  so  a  roundabout 
process  is  employed.  Sodium  chloride  is  first  changed  to 
sodium  sulphate.  It  seems  at  first  sight  that  the  goal  is 
no  nearer,  because  sodium  sulphate  is  just  as  little  acted 
upon  by  carbonic  acid  as  sodium  chloride  is.  But  when 
sodium  sulphate  is  heated  with  a  mixture  of  coal  dust 
and  calcium  carbonate  (limestone),  it  is  reduced  to  sodium 
sulphide,  which  at  the  high  temperature  (1000°  C.)  reacts 
on  the  limestone.  The  process  may  be  represented  by  the 
following  equations: 

2  NaCH- H2SO4  =  NagSO^  4- 2  iTt'/ 

NaaSO^  +  2  C  =  NagS  +  2  00^ 

NagS  +  CfiCOg  =  CaS  4-  NaaCOg 


THE  ALKALI  METALS 


235 


?  In  the 
iter  to  pe- 
er ?  Test 
mperature 
led  in  the 
n.  What 
bave  upon 

bate  made 
in  "  soda  " 
Le  Blanc, 
idemy  for 
>nate  from 
:l  in  1791, 
jeized  and 
it  slightly 
cannot  be 
Dnic  acid, 
)undabout 
hanged  to 
le  goal  is 
ttle  acted 
But  when 
coal  dust 
to  sodium 


3.)  reacts 
:ed  by  the 


The  product  is  called  black  ash,  and  contains  about 
45%  of  sodium  carbonate.  A  small  excess  of  coal  gives 
a  black  or  dark  gray  colour. 

The  mass  is  "lixiviated,"  or  treated  with  a  small  quan- 
tity of  water,  the  sodium  carbonate  is  dissolved,  the  cal- 
cium sulphide  being  left  undissolved. 

The  sodium  carbonate  solution  when  evaporated  forms 
crystals  of  the  formula  Na2C()g,  10  llgO.  We  saw^  that 
when  crystals  of  ice  are  formed  in  salt  water  tlie  ice  con- 
tains very  little  salt.  In  the  same  way,  when  crystals  of 
a  salt  such  as  sodium  carbonate  are  formed,  the  impurities 
are  for  the  most  part  excl'^  led.  Hence,  wlien  a  substance 
contains  impurities  from  which  it  is  desired  to  free  it,  a 
common  method  is  to  dissolve  it  in  water  and  allow  it  to 
crystallise.  What  proportion  of  water  is  there  in  the 
soda  crystals?  When  the  carbonate  is  to  be  sent  to  a 
distance,  it  is  often  more  economical  to  use  fuel  to  drive 
off  the  water  than  to  pay  freight  on  it.  Sodium  car- 
bonate is  called  washing  soda,  because  used  for  laundry 
purposes.  The  dry  salt  is  employed  in  making  glass  and 
was  formerly  used  in  the  preparation  of  metallic  sodium, 
while  from  the  solution,  caustic  soda  is  prepared. 

Another  process  for  making  sodium  carbonate  is  the 
Solvay  or  ammonia  soda  process.  This  process  depends 
upon  the  fact  that  the  acid  sodium  carbonate  NaHCOg  is 
only  sparingly  soluble  in  a  cold  solution  of  sodium  chlo- 
ride containing  ammonia.  So  when  ammonia  is  added 
to  common  salt  solution,  and  carbon  dioxide  passed  into 
the  mixture,  the  reaction  goes  on  as  represented  by  the 
equation 


NaCl  +  NH,  +  ILO  +  QO^  =  NaHCOo  4-  XH/L 


236 


CHEMISTRY 


The  sodium  acid  carbonate  separates  out  in  crystalline 
form.  On  being  heated  it  loses  water  and  half  of  the 
carbon  dioxide,  as  shown  below : 

2  NaHCOg  =  NagCOg  -f-  HgO  +  C0^> 

The  carbon  dioxide  set  free  is  used  with  another  quan- 
tity of  salt  and  ammonia.  The  ammonia  can  be  recovered 
from  the  ammonium  chloride  by  heating  with  lime,  and 
the  lime  is  obtained  from  ttie  limestone  which  supplies 
the  carbon  dioxide.  It  will  be  seen  from  the  following 
equations  how  the  action  goes  : 

CaCOg  =  CaO  +  00^ 
2  NaCl  -f-  2  NHg  +  2  H2O  +  200^  =  2  NaHCOg  +  2  NH^Cl 

2  NaHCOg  =  NaaCOg  +  CO^  +  HgO 
2  NH4CI -}- CaO  =  CaCla  +  2  irag  +  H2O 

In  considering  these  equations  it  must  be  remembered 
that  an  equation  represents  the  obtaining  of  a  certain  defi- 
nite amount  of  various  substances  from  a  given  definite 
amount  of  other  substances.  How  many  molecules  of 
ammonium  chloride  are  represented  as  formed  in  the 
second  equation?  How  many  are  used  in  the  fourth? 
What  is  represented  as  being  made  from  tlie  ammonium 
chloride  in  the  fourth  equation?  What  substances  are 
represented  on  tlie  left-hand  side  of  these  equations  which 
do  not  appear  on  the  right?  What  substances  are  repre- 
sented on  the  right  hand  of  the  equations  that  do  not 
appear  on  the  left  ?  The  substances  on  the  left-hand  side 
are  the  raw  materials;  those  on  the  right-hand  side  are 
the  products  obtained. 

Suppose  we  consider  the  matter  without  reference  to 


crystalline 
alf  of  the 


tlier  quan- 
recovered 
lime,  and 

;h  supplies 
following 


THE  ALKALI  METALS 


23' 


h  2  NH4CI 

3membered 
ertain  defi- 
en  definite 
olecules  of 
led  in  the 
he  fourth? 
ammonium 
stances  are 
dons  which 
are  repre- 
hat  do  not 
t-hand  side 
id  side  are 

jference  to 


equations.  What  is  it  that  the  manufacturer  wishes  to 
obtain  for  the  purposes  of  sale?  From  what  does  the 
metallic  part  of  this  compound  come  ?  From  what  does 
the  salt  radical  part  come  ?  It  is  evident  that  since  matter 
cannot  be  made  from  nothing,  the  metal  and  the  salt  radi- 
cal must  be  supplied  by  the  raw  materials  to  the  same 
extent,  at  least,  as  they  are  made  use  of  in  the  compound 
wanted.  If  supplied  in  larger  amount,  it  would  follow 
that  so  far  as  the  process  under  consideration  is  con- 
cerned there  would  be  a  loss.  Now  the  raw  material 
supplying  the  metallic  part  and  the  raw  material  supply- 
ing the  salt  radical  part  both  have  other  constituents,  and 
these  must  form  one  or  more  products.  It  will  be  seen 
on  consideration  that  calcium  chloride  is  th  3  other  product 
obtained.  If  calcium  chloride  were  needed  to  the  same 
extent  as  sodium  carbonate,  the  process  would  be  excep- 
tionally satisfactory,  but  unfortunately  calcium  chloride 
is  practically  a  waste  product,  and  the  useful  result  of  the 
whole  action  is  that  sodium  carbonate  *.s  obtained. 

In  the  Le  Blanc  process  it  will  be  seen  that  sodium 
chloride  is  constantly  supplied,  just  as  in  the  ammonia 
soda  process ;  but,  besides  this,  sulphuric  acid,  coal,  and 
limestone  are  also  required.  It  will  be  seen  that  the  same 
amount  of  limestone  is  necessary  as  in  the  ammonia  soda 
process,  because  in  both  cases  all  of  the  carbon  dioxide 
comes  from  the  limestone.  In  both  processes  sodium 
chloride  supplies  the  metallic  part  of  the  sodium  carbonate 
and  limestone  supplies  the  salt  radical.  The  carbon  of 
the  coal  in  reducing  sodium  sulphate  produces  carbon 
dioxide,  but  it  is  not  available  for  making  sodium  car- 
bonate, and  is  lost.  The  sulphur  of  the  sulphuric  acid 
ultimately  appears  in  calcium  sulphide,  which,  as  such,  is 


238 


CHEMISTRY 


not  only  valueless,  but  even  a  nuisance,  because  wlien 
exposed  to  the  air  it  yields  sulphuretted  hydrogen.  Many 
efforts  have  been  made  to  recover  the  sulphur  in  order 
to  regenerate  sulphuric  acid,  and  partially  successful 
methods  have  been  invented,  but  the  sulphuric  acid  is 
not  all  recovered. 

Further  observation  of  the  equations  shows  that  hydro- 
chloric acid  is  one  of  the  products.  This  acid  was  at  first 
allowed  to  go  to  waste,  escaping  into  the  air;  but  as  its 
existence  in  the  atmospliere  was  very  obnoxious,  manu- 
facturers were  forbidden  by  law  to  allow  its  escape.  It 
was  then  employed  for  the  manufacture  of  chlorine  used 
in  making  bleaching  powder ;  and  for  many  years  the 
Le  Blanc  process  has  been  able  to  make  a  stand  against 
the  anuiionia  soda  process  only  becanse  the  latter  does  not 
provide  a  convenient  method  for  the  manufacture  of  this 
important  product.  The  ammonia  soda  process  was  made 
practical  b}^  Solvay,  a  Belgian,  in  tlie  year  1803,  and 
entered  into  competition  with  the  Le  Blanc  process,  which 
had  been  in  use  for  seventy  years ;  and  now  half  of  the 
world's  supply  of  sodium  carbonate  is  made  in  this  way. 

Sulphuric  acid  is  needed  in  the  Le  Blanc  process,  and  it 
is  made  on  the  premises.  In  the  manufacture  of  sulphuric 
acid  nitric  acid  is  required,  and  it  is  also  made  on  the 
premises.  As  already  stated,  bleaching  powder  is  also 
produced,  and  hence  a  soda,  or,  as  it  is  often  called,  an 
alkali,  works  is  very  extensive. 

Caustic  soda  is  manufactured  from  sodium  carbonate 
by  the  action  of  ^'  milk  of  lime,"  that  is,  lime  suspended  in 
water. 

The  reaction  is  represented  by  the  equation 

NagCOg  4- Ca(0H)2  =  CaCOg  +  2  NaOH. 


THE  ALKALI  MKTALH 


239 


ause  wlien 
•en.  Many 
ir  in  order 
successful 
ric  acid  is 

that  hydro- 
was  at  first 

but  as  its 
ous,  manu- 
escape.  It 
lorine  used 

ycfirs  the 
-nd  against 
er  does  not 
ure  of  this 
s  was  made 

1863,  and 
>cess,  which 
half  of  the 
this  way. 
cess,  and  it 
f  sulphuric 
tide  on  the 
ler  is  also 

called,  an 

carbonate 
spended  in 


a. 


The  calcium  carbonate  produced  is  a  soliil  and  is  allowed 
to  settle,  while  tlie  caustii;  soda  solution  is  drawn  olf  into 
cast-iron  kettles,  the  water  evaporated,  and  the  caustic 
soda  fused. 

Lately  electrolytic  methods  hav.e  been  used  for  obtain- 
ing caustic  soda.  Connnon  salt  solution  is  electrolysed; 
chlorine  passes  off  at  the  positive  pole ;  and  the  sodium 
set  free  acts  on  water,  producing  caustic  soda.  The  action 
may  be  represented  by  the  equations 

NaCl  =  Na  ■\-  CI 

Na  + H2()  =  Na()II +// 

Are  these  equations  molecular?  Could  they  be  used  in 
exactly  the  same  way  as  our  ordinary  equations  to  calcu- 
late the  volumes  of  the  gases  set  free? 

State  in  words  the  action  of  chlorine  c>n  caustic  soda 
that  is  represented  by  the  following  equation  : 

2  NaOH  +  Cl^  -^  NaOCl  +  NaCl  +  II2O. 

It  is  one  of  the  difficulties  in  the  electrolytic  process  for 
making  caustic  soda  that  chlorine  and  caustic  soda  are 
liable  to  mix.  There  are  various  ways  of  preventing  the 
mixing,  but  they  are  expensive.  It  seems  still  a  little 
doubtful  whether  electrolytic  methods  will  entirely  re- 
place the  other  methods,  but  nearly  all  the  improvements 
now  made  are  in  the  electrolytic  methods.  The  electro- 
lytic method  requires  as  raw  material  only  common  salt 
solution,  and  both  the  products,  caustic  soda  and  chlorine, 
are  very  valuable ;  but  the  apparatus  required  is  costly, 
and  the  action  of  the  chlorine  on  it  is  very  destructive. 


240 


CHEMISTRY 


Experiment  101.  Dissolve  some  sodium  carbonate, 
say  twenty  grammes,  in  twice  its  weight  of  water,  put  into 
a  beaker,  and  pass  into  it  a  stream  of  carbon  dioxide.  A 
good  way  of  carrying  out  the  operation  is  to  have  the 
delivery-tube  of  the  carbon  dioxide  apparatus  attached  to 
a  funnel  which  dips  into  the  carbonate  solution,  as  shown 
in  tlie  figure  (Fig.  84).  What  weight  of  crystallised  car- 
bonate (the  hydrated  salt,  wash- 
ing soda  crystals)  would  be  equiv- 
alent to  the  twenty  grammes  of 
dry  carbonate  ?  What  evidence 
is  there  that  carbon  dioxide  is 
absorbed  by  sodium  carbonate  ? 
If  it  is  not  plain  that  this  is  so, 
devise  some  method  of  deciding 
whether  it  is  or  not.  The  com- 
pound produced  is  sodium  hydro- 
gen carbonate,  more  frequently 
called  sodium  acid  carbonate,  or 
bicarbonate  of  soda.  The  for- 
mula is  NaHCOg.  Why  should 
it  be  called  bicarbonate?  The  most  common  name  of 
all  is  baking  soda. 

Make  an  equation  representing  the  formation  of  sodium 
bicarbonate  b^  the  action  of  carbon  dioxide  on  an  aqueous 
solution  of  sodium  carbonate.  Is  sodium  acid  carbonate 
more  or  less  soluble  than  sodium  normal  carbonate  ? 
What  reason  can  you  give  for  your  opinion  ?  Why  was 
it  suggested  that  you  should  use  a  funnel  in  the  beaker 
rather  than  the  ordinary  delivery-tube  ? 

Until  1807  the  compound  nature  of  caustic  soda,  though 
suspected  by  chemists,  was  not  proved,  but  in  that  year  Sir 


-JML 


Fio.  84 


carbonate, 
er,  put  into 
Lioxide.     A 
o  have  the 
attached  to 
n,  as  shown 
tallised  car- 
salt,  wash- 
Id  be  equiv- 
^rarames  of 
it  evidence 
dioxide  is 
carbonate  ? 
t  this  is  so, 
of  deciding 
The  com- 
lium  hydro- 
frequently 
irbonate,  or 
The  for- 
iVhy  should 
on  name  of 

n  of  sodium 

an  aqueous 

i  carbonate 

carbonate  ? 
Why  was 

the  beaker 

oda,  though 
hat  year  Sir 


THE  ALKALI  METALS 


241 


Humphry  Davy  decomposed  it  by  a  current  of  electricity, 
and  thus  obtained  metallic  sodium.  The  process  was  very 
expensive,  however,  and  another  method  was  afterward 
discovered,  namely,  that  of  heating  sodium  carbonate  witli 
charcoal.  This  process  was  employed  for  a  long  time, 
but  in  1887  was  replaced  by  a  process  invented  by  Castner, 
which  consists  in  heating  caustic  soda  with  carbon.  The 
carbon,  if  introduced  in  the  form  of  charcoal,  would  float 
on  the  surface  of  the  fused  caustic  soda,  and  thus  not  act 
properly ;  hence  it  is  combined  or  intimately  mixed  with 
iron.  The  temperature  required  is  much  lower  than 
when  sodium  carbonate  is  heated  with  charcoal.  The 
reaction  is  represented  by  the  equation 

3  NaOH  +  C  =  NaaCOg  +  3  H  +  Na. 

How  much  of  the  sodium  in  the  caustic  soda  is  obtained 
in  the  metallic  form  ?  Why  is  tl.  e  rest  of  it  not  necessa- 
rily lost  ?  This  new  process  enabled  sodium  to  be  made 
more  cheaply,  the  price  falling  from  $1.25  to  10.75  a  pound. 
This  was  of  great  importance,  because  sodium  was  used  in 
the  manufacture  of  aluminium,  which  at  that  time  came 
prominently  into  notice.  In  1889  Castner  succeeded  in 
producing  sodium  still  more  cheaply  by  the  electrolysis  of 
fused  caustic  soda.  At  the  present  time  nearly  all  of  the 
sodium  of  commerce  is  made  in  that  way,  so  that  there  is, 
to  a  certain  extent,  a  return  to  the  original  method  by 
which  sodium  was  obtained.  Electrical  power  is  much 
cheaper  than  in  Davy's  time,  and  details  of  the  process 
have  been  modified.  In  the  works  where  Castner's  process 
was  first  applied  it  is  possible  to  turn  out  nearly  a  ton  of 
sodium  every  day.  The  price  of  sodium  was  reduced  to 
10.50  a  pound.     But  aluminium  is  not  now  made  by  the 


242 


CHEMISTRY 


action  of  sodium,  but  by  an  electrical  process,  hence  other 
uses  had  to  be  found  for  sodium,  or  its  production  must 
be  largely  curtailed.  At  the  present  time  one  of  the  most 
important  uses  of  sodium  is  in  making  sodium  peroxide, 
which  is  employed  for  bleaching  purposes,  being  more  con- 
venient to  handle  than  peroxide  of  hydrogen,  which  can 
only  be  preserved  in  aqueous  solution,  and  is  therefore 
more  bulky.  From  sodium  peroxide  hydrogen  peroxide 
can  be  made  whenever  it  is  required. 

Potassium.  —  Potassium  is  a  metal  very  like  sodium.  It 
was  first  prepared  by  Davy  in  1807,  by  the  electrolysis  of 
caustic  potash.  Caustic  potash  and  caustic  soda  are  so 
much  alike  that  naturally  when  he  succeeded  in  decom- 
posing one  of  them  and  so  obtaining  the  metal,  he  tried 
to  decompose  the  other.  Potassium  was  the  first  to  be 
obtained ;  afterwards  sodium  was  prepared  in  the  same 
manner. 

In  one  of  your  early  experiments  you  found  which  of 
these  metals  acts  most  readily  on  water.  If  you  have  for- 
gotten, throw  a  very  small  piece  of  each  metal  into  water, 
and  observe  the  result.  Are  potassium  and  sodium  lighter 
or  heavier  than  water?  The  specific  gravity  of  potassium 
is  only  about  eight-ninths  that  of  sodium. 

Experiment  102.  Melt  some  paraffin  wax  in  a  dry 
test-tube  by  putting  the  test-tube  into  boiling  water. 
When  the  paraffin  is  melted,  put  into  it  a  small  piece  of 
potassium.  Into  another  test-tube  witli  paraffin,  in  the 
same  way,  put  a  piece  of  sodium.  Whicli  melts  easier, 
potassium  or  sodium?  An  alloy  of  tlie  two  in  the  proper 
proportions  is  liquid  at  the  ordinary  temperature. 

Potassium  is  much  more  difficult  to  prepare  than  sodium, 
largely  because  its  chemical  reactions  are  more  energetic. 


THE  ALKALI  METALS 


243 


lence  other 
ction  must 
)f  the  most 

I  peroxide, 
\  more  con- 
which  can 
i  therefore 

II  peroxide 

jodium.  It 
itrolysis  of 
oda  are  so 

in  decom- 
al,  he  tried 

first  to  be 
1  the  same 

d  which  of 
u  have  for- 
into  water, 
ium  lighter 
[  potassium 

c  in  a  dry 
ing  water, 
ill  piece  of 
iBn,  in  the 
elts  easier, 

the  proper 
re. 
lan  sodium, 

energetic. 


It  is  therefore  much  more  expensive,  and  so  there  is  a 
much  greater  difference  between  the  price  of  the  metals 
potassium  and  sodium  than  between  the  price  of  caustic 
potash  and  caustic  soda. 

Potassium  compounds  were  formerly  made  chiefly  from 
potassium  carbonate,  obtained  by  lixiviating  wood  ashes  ; 
hence  the  name  potash.  In  Russia  and  America  wood  is 
even  yet  burned  to  a  small  extent  for  the  sake  of  obtain- 
ing potash,  but  at  the  present  time  by  far  the  greater 
quantity  of  potassium  salts  is  made  from  potassium 
chloride  procured  from  the  salt  mines  of  Stassfurt  in 
Germany,  the  process  being  essentially  the  same  as  for 
the  sodium  salts. 

Experiment  103.  Allow  a  piece  of  caustic  soda  and 
of  caustic  potash  to  stand  for  a  few  minutes  in  the  air. 
Which  of  them  has  taken  up  the  more  water  from  the 
air?  Expose  potassium  carbonate  and  sodium  carbonate 
to  the  air  for  an  hour  or  so.  If  the  air  is  damp,  one  of 
them  will  have  taken  up  enough  water  '.o  appear  quite 
moist,  while  the  other  will  not  appear  to  have  al)sorbed 
moisture.  Which  of  the  two^  sodi-um  carbonate  aud  potas- 
sium carbonate,  is  "  deliquescent  '\^  Potassium  nitrate  does 
not  take  up  moisture  from  the  air  so  readily  as  sodium 
nitrate.  Give  one  reason  why  potassium  nitrate  is  used 
in  gunpowder  instead  of  sodium  nitrate. 

Whether  a  salt  of  potassium  or  of  sodium  will  be 
used  for  a  given  purpose  very  often  depends  upon  which 
is  more  easily  obtained  pure,  a  statement  that  usually 
means,  which  salt  will  crystallise  the  easier;  and  it  is 
seldom  that  the  same  salts  of  sodium  and  of  potassium 
are  used  extensively.  For  instance,  potassium  cyanide, 
ferrocyanide,  iodide,  and  permanganate  are  more  common 


244 


CHEMISTRY 


and  important  than  the  corresponding  sodium  salts, 
whereas  sodium  sulphate,  sulphite,  phosphate,  and  acetate 
are  more  used  commercially  than  the  corresponding  potas- 
sium salts.  In  a  few  cascb  the  ditference  between  the 
compounds  of  the  two  metals  is  such  that  both  are  used. 
Caustic  potash  acting  upon  fats  produces  soft  soap,  while 
caustic  soda  under  the  same  conditions  produces  hard 
soap.  Glass  is  a  silicate,  usually  of  lime,  with  either  pot- 
ash or  soda ;  potash  glass  is  liard  and  difficult  to  fuse ; 
soda  glass  is  softer  and  more  fusible.  Silica,  used  in  mak- 
ing glass,  is  obtained  from  pure  sand ;  soda  is  supplied 
either  in  the  form  of  carbonate  or  of  sulphate;  the 
former  fuses  more  easily,  but  the  latter  is  cheaper.  Pot- 
ash is  supplied  as  carbonate,  very  rarely  as  sulphate,  for 
the  latter  does  not  act  well.  Lime  is  obtained  from  chalk 
or  limestone. 

Ammonium.  —  When  ammonia  combines  with  an  acid,  a 
substance  is  produced  very  similar  to  the  salt  produced  by 
the  action  of  the  sam*3  acid  upon  caustic  potash.  When 
caustic  potash  is  added  to  hydrochloric  acid,  potassium 
chloride  is  obtained,  water  being  at  the  same  time  pro- 
duced. Ammonia  and  hydrochloric  aoid  combine  to  form 
a  salt  very  similar  to  potassium  chloride,  and  to  it  the 
name  ammonium  chloride  is  given.  In  the  same  way 
ammonium  sulphate  and  annnonium  nitrate  correspond  to 
potassium  sulphate  and  potassium  nitrate.  The  substance 
ammonium  has  never  been  prepared,  but  the  group  of 
the  elements  nitrogen  and  hydrogen  represented  by  the 
formula  NH^  passes  from  one  compound  to  another. 
Just  as  potassium  chloride  when  acted  on  by  sulphuric 
acid  yields  potassium  sulphate,  so  ammonium  chloride 
acted  on  by  sulphuric  acid   yields  ammonium  sulphate. 


THE  ALKALI   METALS 


245 


mm  salts, 
md  acetate 
iiiig  potas- 
jtween  the 
li  are  used, 
soap,  while 
duces  hard 
either  pot- 
It  to  fuse ; 
ied  in  mak- 
is  supplied 
)hate;  the 
Lper.  Pot- 
ilphate,  for 
from  chalk 

h  an  acid,  a 
roduced  by 
sh.  When 
,  potassium 
!  time  pro- 
ine  to  form 
d  to  it  the 
same  way 
rrespond  to 
le  substance 
e  group  of 
ited  by  the 
0  another. 
y  sulphuric 
m  chloride 
n  sulphate. 


Though  ammonium  itself  has  nut  been  obtained,  an  alloy 
of  it  with  mercury  (ammonium  amalgam)  is  not  difficult 
to  prepare,  though  it  is  difficult  to  preserve. 

ExPEiiiMENT  104.  Into  a  dry  test-tube  put  a  few 
grammes  of  mercury,  then  introduce  a  small  piece  (half 
the  size  of  a  pea)  of  sodium,  cork  the  test-tube  very 
loosely,  and  heat  gently.  There  should  be  a  flash  of  light 
when  the  mercur}^  is  sufficiently  heated,  the  sodium  form- 
ing an  alloy  with  the  mercury.  Hence  care  should  be 
taken  in  the  operation.  Introduce  another  small  })iece 
of  sodium,  and  if  necessary  again  heat,  repeating  the 
process  till  the  mercury  is  seen  to  become  solid ;  then 
remove  from  the  test-tube  (perhaps  you  may  need  to 
break  the  test-tube).  Why  were  you  told  to  cork  tlie 
test-tube  loosely?  The  substance  produced  is  sodium 
amalofam.  What  action  does  it  have  on  water?  What 
are  the  substances  produced  ?  Why  do-^s  the  solid  change 
to  a  liquid?  What  is  the  reaction  toward  litmus  of  the 
water  after  the  amalgam  is  put  into  it?  If  your  pre- 
vious knowledge  does  not  enable  you  to  answer  these 
questions,  make  the  experiments  with  a  small  portion  of 
the  amalgam  that  you  have  prepared.  Then  into  a 
strong  solution  of  ammonium  chloride  in  a  porcelain 
dish  put  another  small  portion  of  your  amalgam.  What 
change  do  you  notice  in  the  amalgam?  How  does  it 
appear  as  compared  with  what  is  obtained  by  the  action 
of  the  amalgam  on  water  alone  ?  Describe  the  feeling  to 
the  fingers  of  the  substance.  The  substance  that  you 
are  examining  is  called  ammonium  amalgam.  Allow  it 
to  .'ind  for  a  few  minutes.  What  change  takes  place 
iri  ■  ?  What  are  the  bubbles  that  aie  coming  off?  In 
order  to  determine  this  point,  put  the  main  portion  of  the 


"m 


246 


CHEMIST  MY 


sodium  amalgam  into  a  test-tube,  fill  three-fourths  of  the 
tube  with  concentrated  ammonium  chloride  solution,  and 

after  the  amalgam  has  ex- 
panded fill  the  test-tube 
to  the  top  with  water,  in- 
vert over  a  vessel  of  water, 
and  collect  tiie  gas  as  in 
Fig.  85.  Test  it  with  a 
lighted  match. 

Lithium,  Rubidium, 
Caesium.  —  These     three 

metals  belong  to  the  same 

group  as  sodium  and  potas- 
sium, lithium  being  less  active,  and  rubidium  ard  cyesium 
being  more  active.  The  last  two  are  on  this  account 
very  difficult  indeed  to  prepare,  and  as  the  salts  even  are 
rare,  the  metals  are  very  expensive.  Caesium  is  the  most 
energetic  of  all  the  metals. 


Fio.  85 


irths  of  the 

)lution,  and 

im  has  ex- 

e   test-tube 

1  water,  in- 

el  of  water, 

gas  as  in 

it  with  a 

Lubidium, 

lese  three 
to  the  same 
a  and  potas- 
and  euesiuni 
his  account 
Its  even  are 
is  the  most 


CHAPTER  XVII 

THE  METALS  OF  THE  ALKALINE  EARTHS 

Experiment  105.  Place  in  separate  watch-glasses,  or 
in  other  convenient  dishes,  small  quantities  of  calcium 
chloride,  strontium  chloride,  and  barium  chloride.  Test 
each  of  them  on  a  platinum  wire  in  the  flame.  Which 
substances  are  most  similar  in  the  colour  of  their  flame  ? 

Pour  about  2  c.c.  strong  sulphuric  acid  into  a  test-tube, 
upon  a  little  calcium  chloride  (about  as  much  as  an  apple 
seed  —  better  in  the  form  of  powder  tha  :  .'n  a  lump). 
What  substances  will  be  produced  by  the  action  of  the 
sulphuric  acid  on  the  chloride? 

Complete  the  equation 

CaClg  >  H2S04  = 

Carefully  heat  the  test-tube  till  the  sulphuric  acid  be- 
gins to  fume,  unless  the  solid  has  previously  dissolved. 
Would  hot  sulphuric  atid  or  hot  water  give  the  worse 
burn  ?  W  hat  conclusion  do  you  come  to  as  to  whether 
calcium  sulphate  is  soluble  in  strong  sulphuric  acid  ? 
After  the  sulphuric  acid  is  cold,  pour  it  into  about  200  c.c. 
of  water.  Notice  whether  or  not  a  precipitate  is  formed. 
Repeat  the  experiment,  using  strontium  chloride  and 
barium  chloride  instead  of  calcium  chloride.  Which  sul- 
phate of  the  three  is  apparently  the  most  readily  soluble 
in  water?     Which  sulphate  is  least  soluble  ? 

247 


248 


CBEMTSTRY 


By  this  time  you  will  probably  notice  that  one  of  the 
chlorides  in  the  watch-glass  has  deliquesced  considerably. 
Which  one  is  it  ?  Allow  the  glasses  to  stand  open  to  the 
air  for  several  days.     Which  ones  now  exhibit  deliques- 


cence 


Tlie  most  important  salts  of  barium  are  barium  sul- 
phate, used  in  the  arts  as  a  pigment  instead  of  white  lead, 
and  barium  chloride,  employed  in  the  laboratory  as  a  test 
for  sulphuric  acid  and  sulphates.  The  most  commonly 
used  salt  of  strontium  is  the  nitrate  employed  for  making 
coloured  lights  (red  fire).  The  compounds  of  calcium 
are  by  far  the  most  important. 

Experiment  100.  Upon  a  piece  of  calcite  (or  if  cal- 
cite  is  not  convenient,  upon  a  piece  of  marble)  put  dilute 
hydrochloric  acid.  What  do  you  observe  ?  Hold  in  the 
gas  produced  a  drop  of  lime-water  on  the  end  of  a  glass 
rod.  What  is  the  gas?  Wrap  one  end  of  a  platinum 
wire  round  a  small  fragment  of  calcite  (lialf  the  size  of 
an  apple  seed)  and  hold  the  calcite  for  two  cr  three  min- 
utes in  a  Bunsen  burner  flame  just  above  the  green  inner 
cone.  What  change  do  you  see  in  the  lump  of  calcite  ? 
Put  the  substance  into  a  dish,  and  allow  a  drop  of  water 
to  fall  upon  it.  What  happens  ?  Add  a  few  more  drops 
of  water,  and  test  the  substance  with  litmus-paper.  How 
does  this  substance  differ  from  calcite  in  respect  to  its 
action  with  litmus  ?  What  reason  have  you  for  consider- 
ing that  by  your  treatment  of  calcite  you  have  obtained 
a  substance  similar  to  caustic  soda  ?  How  could  you  prove 
that  calcite  contains  something  which  is  also  in  calcium 
chloride  ? 

The  operation  which  you  have  performed  on  the  very 
smidl  scale  in  heating  calcite  is  carried  out  on  the  large 


r 


one  of  the 
nsiderably. 
pen  to  the 
t  deliques- 

arium  sul- 
vvhite  lead, 
y  as  a  test 
commonly 
or  making 
of  calcium 

(or  if  cal- 
put  dilute 
riold  in  the 
of  a  glass 
I  platinum 
the  size  of 
three  min- 
^reen  inner 
of  calcite  ? 
3p  of  water 
more  drops 
per.  How 
pect  to  its 
>r  consider- 
7e  obtained 
I  you  prove 
in  calcium 

>n  the  very 
I  the  large 


THE  METALS   OF  THE  ALKALTNE   EARTHS        249 

scale  in  lime  kilns.  Limestone  is  strongly  heated,  and 
quickWmQ  is  produced,  which,  when  acted  on  by  water, 
gives  slaked  lime.  Place  a  i"mp  of  good  quicklime  on  a 
porcelain  plate  or  evaporatii.j  dish,  and  pour  over  it  a 
little  less  than  its  own  volume  of  water.  What  evidence 
have  you  of  energetic  chemical  action  ?  What  change  is 
there  in  the  consistency  of  the  substance  ?  The  reaction 
is  represented  by  the  equation 

CaO  +  \\<P  =  Ca(0H)2. 

Lime  is  .  iai^^ly  used  in  plaster  and  mortar  for  building 
purpose?  bbo  also  in  the  purification  of  coal  gas,  in  the 
tanning  of  leather,  and  in  many  other  operations. 

ExPER  MENT  107.  Shake  up  some  slaked  lime  with 
water  How  would  vou  show  that  thouGfh  slaked  lime 
is  not  very  soluble,  it  is  soluble  to  a  sliglit  extent.  Slaked 
lime  in  suspension  in  water  is  "milk  of  lime"";  the  solu- 
tion separate  from  the  solid  sediment  is  "lime-water." 

Pass  through  clean  lime-Avater  a  current  of  carbon  di- 
oxide. The  cloudiness  first  produced  is  due  to  calcium 
carbonate,  which  is  practically  insoluble  in  water.  Pass 
the  carbon  dioxide  still  longer  till  the  precipitate  dis- 
solves. Did  we  find  in  a  former  experiment  that  aodium 
bicarbonate  is  more  or  less  soluble  than  sodium  carbonate? 
What  conclusion  do  you  now  draw  regarding  calcium 
bicarbonate  as  compared  with  calcium  carbonate?  Mix 
about  equal  volumes  of  bicarbonate  solution  and  of  the 
original  lime-water.  Why  do  you  get  a  precipitate  ? 
Filter  off  the  precipitate.  Does  the  filtrate  contain  as 
much  lime  as  an  equal  volume  of  bicarbonate  solution? 

Make  a  solution  of  soap,  add  a  little  to  the  water  con- 
taining calcium  bicarbonate  (bicarbonate    of   lime),  and 


250 


CHEMISTRY    ' 


shake.  The  appearance  produced  is  that  caused  by  hard 
water.  Add  some  soap  solution  in  the  same  way  to  the 
filtrate  mentioned  above,  and  you  should  find  it  easier  to 
produce  a  lather.  The  water  has  been  made  less  hard. 
In  limestone  districts  the  water,  especially  in  wells,  is 
hard,  because  the  limestone  (calcium  carbonate)  dissolves 
in  the  water  of  the  soil  which  always  contains  carbon 
dioxide.  Such  water  may  be  softened  by  adding  lime- 
water,  and  allowing  the  precipitate  formed  to  settle  ;  so 
that  we  have,  what  at  first  seems  strange,  the  fact  that 
water  which  is  hard  because  it  contains  a  compound  of 
lime  may  sometimes  be  made  soft  by  adding  lime. 

Heat  some  of  the  bicarbonate  solution.  What  evidence 
have  you  that  the  bicarbonate  is  decomposed  by  heat  ? 
Why  should  water  in  some  cases  be  softened  by  boiling  ? 
Water  is  sometimes  hard  because  containing  calcium  sul- 
phate ;  such  water  is  not  softened  by  either  of  the  above 
methods  which  are  effectual  w4th  bicarbonate,  and  is  said 
to  have  permanent  hardness,  while  the  hardness  due  to 
bicarbonate  is  temporary/. 

Experiment  108.  Heat  some  gypsum  in  a  test-tube. 
What  is  driven  off  from  it?  If  the  gypsum  is  in  the 
form  of  a  transparent  crystal  (selenite)  notice  the  change 
in  appearance.  Heat  some  powdered  gypsum  for  five  or 
ten  minutes  in  a  porcelain  dish,  keeping  the  flame  moving 
under  it,  so  that  it  will  not  become  very  hot  in  any 
part.  The  temperature  should  not  rise  above  200°  C,  and 
125°  C.  is  best.  Mix  the  powder  so  obtained  with  about 
one-third  its  weight  of  water,  and  allow  to  stand.  You 
should  find  that  the  powder  takes  up  water,  and  hardens 
or  sets  into  a  solid  mass.  You  have  made  "plaster  of 
Paris."     Heat  another  portion  of  gypsum  to  a  red  heat. 


THE  METALS  OF  THE  ALKALINE  EAIiTHS        251 


d  by  hard 
vay  to  the 

easier  to 
less  hard. 

wells,  is 
)  dissolves 
ns  carbon 
ing  lime- 
settle  ;  so 
fact  that 
ipound  of 
e. 

t  evidence 
by  heat  ? 
y  boiling  ? 
Icium  sul- 
the  above 
md  is  said 
!ss  due  to 

test-tube. 

is  in  the 
he  change 
for  five  or 
le  moving 
ot  in  any 
0°  C,  and 
ith  about 
nd.  You 
d  hardens 
plaster  of 

red  heat. 


How  does  the  substance  obtained  act  with  water  ?  In  the 
first  case  you  drove  out  approximately  three-fourtlis  of 
the  water  from  the  gypsum  ;  in  the  second  case  you 
drove  out  all  of  the  water.  The  mineral  anhydrite  is 
calcium  sulphate  without  water.  Why  can  it  not  be  used 
for  making  plaster  of  Paris  ? 

A  very  important  compound  of  calcium  is  bleaching 
powder,  obtained  by  passing  chlorine  over  slaked  lime. 
The  name  chloride  of  lime  has  been  given  to  it.  The 
precise  nature  of  the  compound,  in  other  words  its  con- 
stitution, is  not  thoroughly  understood  ;  but  when  dis- 
solved in  water  it  forms  calcium  chloride  and  calcium 
hypochlorite,  and  the  hitter,  or  the  hypochlorous  acid  or 
chlorine  produced  from  it,  is  what  bleaches.  Exactly 
what  is  produced  depends  upon  the  treatment  to  ^\hich 
the  chloride  of  lime  is  subjected. 

Calcium,  strontium,  and  barium  produce  hydrates  which 
are  alkaline  like  those  of  potassium  and  sodium,  and,  on 
the  other  hand,  they  form  compounds  having  a  character 
which  we  call  earthy,  and  hence  the  metals  are  called 
metals  of  the  alkaline  earths. 

Compounds  of  calcium,  strontium,  and  barium  fre- 
quently crystallise  in  the  same  form,  or  are  isomorphous^ 
and  in  many  cases  the  compounds  of  lead  are  isomorphous 
with  them.  In  some  respects  lead  is  similar  to  the  alka- 
line earths,  but  it  is  more  closely  allied  to  tin. 


CHAPTER   XVIII 


THE  ZINC  GROUP  OF  METALS 


There  is  another  group  of  elements  somewhat  con- 
nected with  those  just  considered.  They  are  for  the  most 
part  bivalent,  so  that  the  formulae  of  their  compounds  are 
written  in  the  same  manner.  The  metals  are  magnesium, 
zinc,  cadmium,  and  mercury.  Magnesium  carbonate  and 
to  a  certain  extent  the  other  carbonates,  when  they  exist, 
are  similar  to  those  of  calcium,  strontium,  and  barium. 
But  the  sulphates  are  for  the  most  part  very  soluble, 
unlike  those  of  the  alkaline  earths,  and  the  metals  them- 
selves are  much  more  easily  prepared  than  those  of  the 
previous  group.  The  properties  of  the  metals  have  a 
very  noticeable  gradation.  They  do  not  act  on  water  at 
the  ordinary  temperature,  but  magnesium  and  zinc  both 
act  on  water  vapour  at  a  high  temperature,  magnesium 
more  readily  than  zinc.  Magnesium  is  the  hardest  and 
cadmium  the  softest  of  the  three  solid  metals.  The  spe- 
cific gravity  goes  in  the  order,  magnesium,  zino,  cadmium, 
and  mercury.  On  the  other  hand,  the  fubjbility  and 
volatility  are  in  the  exact  reverse  order,  mercury  being 
a  liquid,  at  the  ordinary  temperature,  while  magnesium 
requires  quite  a  high  temperature  to  melt  it.  Magnesium 
has  a  considerable  affinity  for  oxygen,  and  when  heated 
burns  very  brilliantly  in  air,  the  light  being  used  for 
photographic  purposes.      Zinc  does  not  oxidise  quite  so 

252 


THE  ZINC  GROUP  OF  METALS 


253 


what  con- 
31'  the  most 
pounds  are 
nagnesium, 
bonate  and 

they  exist, 
id  barium, 
ry  soluble, 
etals  them- 
lose  of  the 
als  have  a 
^n  water  at 
I  zinc  both 
magnesium 
lardest  and 
The  spe- 
\  cadmium, 
Jbility  and 
cury  being- 
magnesium 
Magnesium 
lien  heated 
J  used  for 
56  quite  so 


readily,  but  it  also  burns  'orilliantly,  especially  if  heated 
in  pure  oxygen.  Cadmium  oxidises  at  a  high  temperature 
in  the  air,  but  not  so  easily  as  the  other  elements.  ^ler- 
cury  oxidises  perceptibly  if  ke[)t  at  a  temperature  250°  ('.- 
800°  C.  for  several  days,  but  the  oxide  decomposes  at  a 
slightly  higher  temperature. 

The  relative  tendency  to  combine  with  oxygen  is  seen 
in  the  minerals  containing  the  elements.  Magnesium  is 
found  as  carbonate  either  alone  or  with  calcium  carbonate, 
also  as  sulpiiate  (Epsom  salts),  as  silicate  in  talc  (French 
clialk),  asbestos,  and  meerschaum,  but  not  as  sulpliide. 
Zinc  is  also  found  as  carbonate  and  silicate,  but  the  most 
important  ore  is  the  sulphide  (zinc  blende).  Cadmium  is 
frequently  found  in  small  quantity  in  zinc  ores,  chiefly 
blende,  but  the  only  pure  mineral  known  is  tlie  sulphide. 
Mercury  is  mainly  found  as  sulphide  (cinnabar),  also  in 
the  metallic  form,  but  not  combined  with  oxygen.  The 
metallurgy  of  the  metals  illustrates  the  relative  affinities 
for  oxygen.  When  cinnabar  is  roasted,  the  oxygen  of  the 
air  combines  with  the  sulphur  and  the  mercury  volatilises. 
Cadmium  and  zinc  sulphides  are  roasted  to  change  them 
to  oxide,  and  the  oxide  is  heated  with  charcoal.  Mag- 
nesium oxide  cannot  be  reduced  in  this  way.  The  method 
used  till  lately  was  to  heat  the  chloride  with  sodium,  the 
reaction  following  the  course  indicated  by  the  equation 

MgCl2  +  2  Na  =  Mg  +  2  NaCl. 

The  method  used  by  Bunsen  and  now  largely  employed, 
is  to  electrolyse  the  double  chloride  of  magnesium  and 
potassium,  the  magnesi'  m  being  set  free  more  easily  than 
the  potassium.  Thou  ;^  minerals  containing  magnesium 
are  the  most  common  and  are  the  cheapest,  the  metal  itself 


254 


CHEMISTRY 


is  by  far  the  most  expensive,  costing  more  than  ten  times 
as  much  as  zinc.  Mercury  and  cadmium  are  more  expen- 
sive than  zinc,  the  ores  being  less  common,  but  they  cost 
little  more  than  half  as  much  as  magnesium. 

The  salts  of  magnesium,  while  being  bitter,  are  not 
in  the  ordinary  sense  poisonous ;  those  of  zinc  are  nau- 
seating ;  while  the  salts  of  mercury,  having  a  similar 
composition,  are  violent  poisons  when  taken  inwardly. 
Mercuric  chloride  (corrosive  sublimate)  has  a  very  poi- 
sonous action  upon  microbes.  Some  microbes  by  their 
growth  cause  suppuration  in  a  wound  or  in  any  part  cut 
open  by  a  surgeon.  Mercuric  chloride  has  a  very  poison- 
ous action  upon  these  microbes,  and  a  solution  dilute 
enough  not  to  hurt  the  tissues  of  the  body,  but  strong 
enough  to  kill  the  microbes,  is  used  for  washing  out 
wounds,  healing  being  thus  promoted. 

The  gradation  of  properties  which  v/e  have  noticed 
corresponds  with  a  gradation  in  the  atomic  weights. 
Magnesium  has  the  lowest  atomic  weight,  then  zinc, 
afterward  cadmium,  and  finally  mercury.  There  is  a 
similar  gradation  in  many  of  the  properties  of  the  alka- 
line earth  metals.  What  is  the  order  of  the  solubilities 
of  the  sulphates  of  calcium,  barium,  and  strontium  ? 

Mercury  has  some  properties  distinctly  differing  from 
those  of  the  other  metals  of  the  group.  It  forms  two 
classes  of  compounds,  —  the  mercuric  salts,  which  are  in 
many  respects  similar  to  those  of  magnesium,  zinc,  and 
cadmium,  and  the  mercuroits  salts,  which  have  no  analo- 
gies among  the  salts  of  the  other  metals.  In  the  mercuric 
salts  mercury  acts  as  a  bivalent  element ;  in  the  mercurous 
salts  the  compounds  are  such  as  would  be  formed  by  a 
monovalent  element.     Mercurous  chloride  has  the  formula 


THE  ZINC  GROUP   OF  METALS 


255 


ten  times 

)re  expen- 

they  cost 

•,  are  not 
1  are  nau- 

a  similar 
inwardly. 

very  poi- 
1  by  their 
y  part  cut 
ry  poison- 
Lon  dilute 
>ut  strong 
sliing  out 

e  noticed 
weights. 
:hen  zinc, 
here  is  a 
the  alka- 
olubilities 
im  ? 

ring  from 
'orms  two 
Lch  are  in 
zinc,  and 
no  analo- 
;  mercuric 
inercurous 
med  by  a 
le  formula 


HgCl,  while  that  of  mercuric  chloride  is  HgClj.  Mer- 
curous  chloride  is  insoluble  in  water,  in  this  respect 
resembling  silver  chloride. 

Magnesium  has  a  number  of  uses,  but  the  most  impor- 
tant is  as  an  illuminant  for  fliish  lights  and  similar  pur- 
poses. Zinc  is  employed  as  a  coating  for  iron  goods, 
so-called  "  galvanised  iron  "  being  sheet-iron  coated  with 
zinc  to  prevent  rusting.  It  is  a  constituent  of  brass  and 
of  German  silver.  Mercury  is  largely  used  in  the  extrac- 
tion of  gold  and  silver  from  their  ores,  forming  with  these 
metals  an  amalgam  from  which  the  mercury  is  afterward 
volatilised  and  recovered.  Many  amalgams  are  useful, 
some  being  employed  for  filling  teeth  and  some  in  making 
mirrors.  Pure  mercury  is  used  in  thermometers  and 
barometers.  Cadmium  is  the  least  useful  of  the  four 
metals. 


CHAPTER   XIX 


THE   IRON   GROUP  OF  METALS 


Iron.  —  Iron  is  the  most  important  of  the  metals,  about 
forty  million  tons  a  year  being  smelted,  one-third  of  it  in 
the  United  States.  Iron  is  sometimes  found  native,  but 
not  in  sufficient  quantity  to  be  more  than  a  curiosity, 
being  mainly  of  meteoric  origin.  In  compounds  it  is 
very  widely  distributed,  the  reddish  tint  in  weathered 
rocks  being  due  to  iron  in  a  form  similar  to  that  of  rust. 
But  iron  compounds  must  contain  the  iron  in  large  quan- 
tity, and  in  a  form  easy  to  extract  before  they  can  be 
economically  used  as  ores  of  i  m.  The  most  important 
ores  are  the  oxides  and  the  carbonates.  There  are  two 
important  oxides,  —  magnetite,  which  when  pure  contains 
72.4  %  of  iron,  being  represented  by  the  formula  FcgO^, 
and  hematite,  containing  70  %,  its  formula  being  FcgOg. 
Magnetite  is  nearly  bla^di,  is  brittle,  heavy,  and  magnetic. 
Hematite  is  non-magnetic,  in  general  reddish,  and  for  the 
most  part  not  quite  so  heavy  as  magnetite.  Limonite, 
sometimes  called  brown  hematite,  contains  water  as  well 
as  the  oxide  found  in  hematite.  It  is  not  so  heavy  as 
hematite,  and  has  a  yellowish  colour  when  scratched,  thus 
being  distinguished  from  hematite,  which  is  red  when 
scratched.  Siderite  is  ferrous  carbonate,  FeCOg,  contain- 
ing when  pure  48.27  %  of  iron.  Clay  iron  stone  contains 
clay  mixed   with  siderite,  and   in  black  band  siderite  is 

256 


THE  IliON   GROUP   OF  METALS 


257 


3tals,  about 
ird  of  it  in 
native,  but 
I  curiosity, 
Junds   it  is 

weathered 
lat  of  rust, 
arge  quan- 
ley  can  be 
'  important 
ire  are  two 
re  contains 
lula  FcgO^, 
ing  FegOg. 
.  magnetic, 
md  for  the 

Limonite, 
ter  as  well 
)  heavy  as 
iched,  thus 

red  when 
>g,  contain- 
le  contains 
siderite  is 


mixed  with  carbonaceous  material,  in  some  cases  to  such 
an  extent  that  little  fuel  is  necessary  in  the  reduction  of 
the  metal. 

The  ores  of  iron  usually  contain  impurities,  such  as 
silica  and  silicates,  and  these  must  be  removed.  The  most 
important  method  for  reducing  iron  from  its  ores  is  tliat 
of  the  blast  furnace.  The  blast  furnace  is  built  of  a 
specially  infusible  brick,  to  which  tlie  name  lire-brick  is 
given.  Its  sliape  is  that  of  a  double  cone,  the  lower  cone 
being  the  shorter,  as  shown  in  the  figure  (Fig.  ^<')).  It 
is  sometimes  eighty  to  a  hundred  feet  in  height,  and  fif- 
teen or  twenty  feet  in  greatest  width.  The  fuel  (coke, 
coal,  or  charcoal)  is  introduced  at  the  top,  together  with 
the  iron  ore  and  the  material  wliich  is  to  remove  the 
impurities.  The  most  important  of  the  flnj-ea  added  is 
limestone,  since  it  combines  with  silica,  and  forms  a  fusi- 
ble slag,  leaving  the  iron  comparatively  pure.  The  air  to 
support  the  combustion  is  sent  as  a  blast  into  the  lower 
part  of  the  furnace,  jn?*^  above  the  place  where  the  molten 
metal  and  slag  are  to  be  collected.  Tlie  blast  enters 
through  tuyeres  (pronounced  iweers)^  which  arc  iron  i)ipes, 
whose  number  differs  in  different  furnaces,  and  whose  size 
also  varies.  The  air  is  heated  before  being  sent  into  the 
furnace,  so  that  the  temperature  of  tlie  furnace  may  be 
kept  higher  than  would  be  [)ossible  with  a  cold  blast. 
The  reactions  that  take  place  in  the  furnace  are  com})!!- 
cated,  but  consist  essentially  in  the  change  f»f  caribou  (\io\- 
ide  into  (;arbon  monoxide  by  contact  with  carbon,  and  of 
carbon  monoxide  into  carbon  dioxide  by  the  action  of  the 
iron  oxides.  The  carbon  dioxide  is  in  the  lirst  place  pro- 
duced by  the  burning  of  the  fuel  in  excess  of  air,  and  by 
the  heating  of  the  limestone.     As  the  iron  ore  gives  up 


■  'AT, 


258 


CUEmSTRT 


its  oxygen  to  the  f'jel  it  is  redu(ie(l  to  metallic  iron,  wLich 
combines  with  a  certain  quantity  of  carbon,  and  also  with 
a  small  amount  of  silico:i  and  other  substances,  reduced 
at    the   same   time   from,   the   impurities    present.      The 


Fig.  86 

greater  part  of  the  imj)urities  combines  with  the  lime 
of  the  limestone  and  produces  the  slag,  a  molten  mass 
which  is  not  so  heavy  as  molten  iron,  and  collects  on  the 
top  of  it.  There  are  thus  at  the  bottom  of  the  furnace 
two  molten  layers, —  iron  beneath  and  slag  above.    Every 


THE  IRON  GROUP  OF  METALS 


259 


iron,  which 
ad  also  with 
ces,  reduced 
isent.      The 


th  the  lime 
molten  mass 
lects  on  the 
the  furnace 
ove-.    Every 


few  hours  these  two  layers  are  iv;ii  oft  ''rom  the  furnace 
through  tap  holes,  which  are  at  '.  thei  times  kept  plugged 
with  clay. 

The  iron  is  run  into  moulds, ".  iunlly  made  of  sand,*  and 
is  thus  shaped  into  bars  or  pir/s.  This  is  ednt-iroyi,  and 
contains  carbon  and  silicon,  with  occasionally  phosphorus 
and  sulphur.  The  carbon  in  pig-iron  sometimes  amounts 
to  as  much  as  41  %•  It  may  be  either  combhied  with 
the  iron  or  diffused  through  it  in  crystalline  scales. 
When  the  carbon  is  mainly  combined  the  iron  is  ichite  ; 
when  it  is  mainly  free  the  iron  is  gray  ;  when  partly  com- 
bined and  partly  free  the  iron  is  mottled.  Iron  cooled 
rapidly  is  white,  because  rapid  cooling  does  not  give  time 
for  the  separation  of  crystals.  White  iron  is  harder  than 
gray  iron. 

It  is  in  general  true  that  alloys  melt  at  a  lower  'em- 
perature  than  pure  meials,  vi\<\  cast-iron  melts  more 
readily  than  pure  iron.  Moreover,  when  it  solidities  it 
expands  somewhat,  and 
is  therefore  suitable  fo»- 
making  casts  taking  tht 
form  of  the  mould.  In 
making  a  casting  the 
metal  is  melted,  and  rim 
into  a  mould  of  the  re- 
quired form.  Cast-iron 
is  more  brittle  than  pure 
iron,    and     cannot     be 

hanunered  or  beaten  into  shape  as  the  latter  can.     This 
purer  iron,  wrought-iroiu  is  made  horn  pig-iron  by  mclt- 

*In  lai^e  works  the  iron  is  sometimes  run  >nto  large  receptacles, 
where  it  is  kept  liquid  till  ready  for  conversion  into  steel. 


Fi<i.  87 


260 


CHEMISTRY 


ing  tli(3  latter  and  heating  it  in  such  a  manner  that  the 
impurities  are  oxidised  and  removed.  The  process  is 
carried  out  in  a  puddling  furnace,  the  shape  of  which  is 
shown  in  the  figure  (Fig.  87).  The  fuel  is  in  a  grate, 
separated  from   the   metal,  which  is  melted   by  the  liot 

flame  reflected 
from  the  roof 
of  the  hearth 
upon  the  iron. 
Owing  to  its 
form  the  fur- 
nace is  called 
a  reverberator y 
furnace.  Along 
with  the  gases 
from  the  grate, 
hot  air  strikes 
upon  the  pig- 
ircn  and  oxi- 
dises the  impu- 
rities, which  are 
removed  in  the 
slag.  As  the 
i  ron  becomes 
purified  it  melts 
less  easily,  and 
becomes  pasty. 
When  the  impurities  are  nearly  all  oxidised  the  iron  is 
removed  in  lumps,  and  hammered  or  squeezed  to  press  out 
tlie  slag  and  weld  tlie  mass  together.  A  form  of  hammer 
is  shown  in  Fis^.  88.  Wrou<j^ht-iron  is  fibrous  in  its 
structure,  is  ductile,  malleable,  tough,  and  soft.     It  cannot 


Fig.  88 


rnE  iBos  GRorr  or  metals 


261 


ler  that  the 

process    is 

of  which  is 

in  a  grate, 

by  tlie  liot 

le     reflected 

the    roof 

the     hearth 

n    the   iron. 

mg     to     its 

11     the    fur- 

3     is    called 

'everheratory 

nace.   Along 

1   the   gases 

n  the  grate, 

air    strikes 

n    the    pig- 

i    and     oxi- 

!S  the  impu- 

3S,  which  are 

oved  in  the 

As    the 

L    becomes 

ified  it  melts 

easily,  and 

)mes    pasty. 

the  iron  is 

to  press  out 

of  hammer 

)rous   in  its 

.     It  cannot 


be  hardened  by  rapid  cooling.  Two  pieces  of  wrouglit- 
iron,  heated  to  a  pasty  condition,  may  bo  welded  by  pres- 
sure or  liammering,  thus  forndng  one  piece. 

Steel  contains  less  carl)on  than  cast-iron,  and  more  tlian 
wrought-iron.  Other  substances,  such  as  nickel  and  man- 
ganese, are   sometimes   added  to  it.     The  properties   of 


100         50 

Li  I  I  I  I  I 


0 


X 


jMeter 


Fig.  81) 

steel  depend  partly  upon  the  nature  and  quantity  of  the 
substances  contained  in  it,  and  partly  upon  the  maimer 
of  tempering.  Ordinary  steel  contains  from  O.lo  %  to 
1.8  %  of  carbon.  It  was  formerly  made  from  wrought- 
iron,  ])y  heating  it  in  a  bed  of  charcoal  for  a  fortnight  or 
longer.  Steel  made  l)y  this  method  is  expensive,  and  now 
nearly  all  of  the  steel  manufactured  is  produced  by  the 


110* lijWn   i-*iMtf.0U^', 


262 


CHEMISTRY 


Bessemer  process.  This  process  consists  in  blowing  air 
through  a  quantity  of  molten  cast-iron  in  a  '*  converter  '* 
of  the  shape  sliown  in  the  figure  (Fig.  89).  When  the 
carbon  is  practically  all  removed  a  certain  quantity  of 
spiefjeleisen^  an  alloy  of  iron  containing  a  considerable 
amount  of  carbon  and  manganese,  is  added,  so  as  to  intro- 
duce the  proper  qu'rintity  of  carbon.  The  presence  of 
manganese  is  advantageous.  Sometimes  carborundum,  a 
compound  of  carbon  and  silicon,  is  added. 

Steel  is  in  general  finely  granular  in  structure,  not 
having  the  fibrous  character  of  wrought-iron,  though  if 
broken  by  a  slow-acting  stress  it  has  a  somewhat  fibrous 
appearance.  Steel  when  suddenly  cooled  by  dipping  it 
into  a  liquid,  such  as  water  or  oil,  becomes  very  hard, 
and  the  hardened  steel  is  tempered  by  heating  carefully 
to  a  temperature  between  220°  C.  and  316°  C.  The  higher 
the  temperature  to  which  the  steel  is  heated  in  tempering 
the  softer  it  becomes,  because  at  the  higher  temperature  the 
particles  of  the  steel  become  more  readily  rearranged. 

Iron  forms  two  classes  of  compounds,  —  the  ferrous  and 
ferric.  Which  compounds  have  the  greater  proportion  of 
iron?  Ferrous  chloride  has  tlie  formula  FeClg  and  ferric 
chloride  the  formula  FeClg ;  the  corresponding  oxides  are 
FeO  and  Yefi^.  In  order  to  illustrate  the  difference,  per- 
form the  following: 

Experiment  109.  Dissolve  some  iron  tacks  in  dilute 
sulphuric  acid,  filter  the  solution,  and  divide  the  filtrate 
into  several  parts.  To  the  first  add  caustic  soda  solution. 
What  is  the  colour  of  the  precipitate  ?  It  is  almost  en- 
tirely ferrous  hydrate,  but  slightly  oxidised  by  the  oxygen 
of  the  air. 

FeSO^  4-  2  NaOH  =  NajSO^  +  Fe(0H)2. 


^ 


lowing  air 
ionverter  " 
When  the 
uantity  of 
)nsiderable 
IS  to  intro- 
resence  of 
)rundum,  a 

icture,  not 

though  if 

hat  fibrous 

clij^ping  it 

very  hard, 

g  carefully 

The  higher 

.  tempering 

)erature  the 

anged. 

ferrous  and 

oportion  of 

2  and  ferric 

oxides  are 

3rence,  per- 

;s  in  dilute 
the  filtrate 
la  solution, 
almost  en- 
the  oxygen 


THE  IROy    GROUP   OF  METALS 


263 


To  another  portion  of  the  solution  add  slowly  a  solution 
of  potassium  permanganate.  Notice  wlit^ther  the  perman- 
ganate colours  the  solution  at  first,  and,  if  not,  ^vhether  it 
is  possible  to  add  enough  permanganate  to  give  a  colour. 

To  a  third  portion  of  the  solution  add  a  few  drops  of 
nitric  acid.  What  change  takes  place  in  the  solution  ? 
Heat  gently.  Divide  this  solution  into  two  parts  and  add 
to  one  of  them  caustic  soda.  How  does  the  precipitate 
compare  in  appearance  with  that  obtained  before  ?  To 
the  second  portion  add  a  few  drops  of  potassium  perman- 
ganate. What  effect  is  produced  by  the  permanganate  ? 
Nitric  acid  is  an  oxidising  agent,  and  in  the  presence  of 
excess  of  sulphuric  acid  changes  ferrous  sulphate  into  fer- 
ric sulphate,  in  which  caustic  soda  produces  ferric  hydrate. 

Fe2(S04)3  -f  6  NaOH  =  3  ^a^SO^  +  2  Fe(0H)3. 

Potassium  permanganate  is  also  an  oxidising  agent,  and 
when  added  to  the  acid  ferrous  sulphate  solution  gives 
up  its  oxygen,  forming  a  colourless  solution,  and  it  is  only 
when  all  of  the  iron  is  changed  to  the  ferric  condition 
that  the  violet  colour  of  the  permanganate  is  seen.  But 
when  the  iron  has  been  all  oxidised  by  nitric  acid  or 
otherwise,  the  permanganate  is  not  required  to  oxidise  it, 
and  the  violet  colour  appears  on  the  addition  of  a  few 
drops. 

Nickel  and  Cobalt.  —  Nickel  and  cobalt  are  in  many 
respects  like  iron,  but  they  are  not  so  common  nor  so 
important.  Nickel  is  found  in  an  oxidised  form  as  sili- 
cate, but  the  most  important  ore  contains  it  as  a  sulphide 
along  with  iron,  often  mixed  with  a  copper  ore.  The  sul- 
phide is  less  easily  oxidised  than  iron  sulphide,  and  along 
with  copper  sulphide  is  separated  from  iron  by  oxidising 


264 


CIIimiSTRY 


the  latter  and  removing  it  in  a  sla<^.  'J'he  nickel  is  after- 
ward separated  from  the  copper.  Nickel,  when  heated  in 
a  current  of  carbon  monoxide  to  a  temperature  of  50°  C, 
forms  a  gaseous  compound  Ni(C0)4,  which  decomposes 
at  180°  C,  yielding  pure  nickel.  This  property  luis  lately 
been  used  as  a  method  of  [)reparing  pure  nic  kel. 

Nickel  does  not  oxidise  so  readily  as  iron,  and  is  used 
as  a  plating  to  keep  iron  and  steel  irom  rusting.  A 
small  percentage  of  nickel  renders  steel  very  hard  and 
tough  and  specially  suitable  for  the  armour  of  warships. 
Another  advantage  is  that  the  alloy  of  iron  with  nickel  is 
less  affected  by  changes  of  temperature ;  therefore  ships 
and  other  heavy  structures  are  less  strained  when  nickel 
steel  is  used  in  their  construction.  Cobalt  is  commer- 
cially not  so  important  as  nickel.  Both  metals  are  mag- 
netic, but  not  so  magnetic  as  iron. 

Manganese.  —  Manganese  is  also  somewhat  similar  to 
iron,  though  its  compounds  are  for  the  most  part  different. 
The  metal  itself  is  not  largely  used,  but  when  added  to 
steel  makes  it  very  hard.  Manganese  forms  some  oxides 
that  are  acid  in  character,  and  one  of  the  most  impor- 
tant compounds  of  manganese  is  potassium  permanganate 
KMnO^,  a  powerful  oxidising  agent  used  as  a  disinfect- 
ant, also  in  bleaching  and  dyeing  and  in  medicine. 

Aluminium.  —  Aluminium  is  a  chief  constituent  of  clay, 
one  of  the  most  common  minerals.  The  metal  is  very 
difficult  to  extract  from  its  ores,  because  aluminium  has 
such  a  strong  affinity  for  oxygen.  Hence,  though  alu- 
minium was  first  separated  in  1827,  it  was  for  sixty  years 
little  more  than  a  curiosity.  It  was  not  found  possible, 
as  in  the  case  of  iron,  to  remove  oxygen  from  the  oxide 
by   means   of   carbon   in  the  ordinary  furnace,  and   the 


el  is  after- 
hi;at('(l  in 
ot:  50°  C, 

ecomposes 
Y  has  lately 


77//';  //.'O.v  (nawv  of  metals 


265 


nd  is  used 
>ting.  A 
liard  and 
warships, 
h  nickel  is 
efore  ships 
hen  nickel 
s  commer- 


s  are  mag- 


similar  to 
•t  different, 
n  added  to 
3me  oxides 
lost  impor- 
manganate 
t  disinfect- 
licine. 
3nt  of  clay, 
bal  is  very 
linium  has 
lough  alu- 
lixty  years 
1  possible, 

the  oxide 
;,  and  the 


method  emjdoyed  for  preparing  (lie  inotal  was  lieating 
aluminium  cldoride  with  sodium.  \ow,  however,  in  the 
electrical  fnrnace,  the  oxide,  usually  in  the  pl•(^s('nce  of 
molten  cryolite  (a  double  ihioride  of  sodium  and  alu- 
minium), is  reduced  and  nu'tallic  aluminium  obtained. 
It  is  a  white  metal  and  very  light,  having  a  specific  grav- 
ity 2.6.  It  is  very  ductile  and  malleable  and  a  good 
conductor  of  electricity.  So  it  is  in  some  respects  a 
substitute  for  iron  and  in  some  for  copper.  It  is  used 
largely  as  an  electric  conductor,  also  for  the  vibrating 
parts  of  macldnery,  and  is  replacing  lithographic  stone. 
Its  uses  are  becoming  more  and  more  numerous  and  will 
increase  with  every  diminution  of  price. 

One  of  the  most  im[)ortant  compounds  of  alaminium  is 
alum  KgSO^,  A  12(804)3,  24  Hfi.  It  is  extensively  used 
in  dye  works  as  a  mordant.,  that  is,  as  a  substance  to  fix 
the  colouring  matter  in  cloth.  Aluminium  sulphate, 
"  paper-makers'  alum,"  is  now  largely  replacing  ordinary 
alum  in  industrial  processes. 

Chromium.  —  Chromium  is  an  element  in  some  respects 
like  aluminium,  forming  compounds  similar  to  ordinary 
alum.  These  compounds  are  used  as  mordants  and  in 
tanning.  The  most  important  salt  is  potassium  dichro- 
mate,  K2C'i'2^\'  ^^^  oxidising  agent  used  in  making  coal  tar 
dyes,  in  bleaching,  in  dyeing,  and  in  the  preparation  of 
leather.  Other  compounds  are  used  as  pigments,  for 
example,  chrome  yellow,  PbCrO^.  Cliromium  in  the 
metallic  state  is  used  in  making  steel. 


IMAGE  EVALUATION 
TEST  TARGET  (MT-S) 


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Hiotographic 

Sciences 

Corporation 


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CHAPTER   XX 


METALS  OF  THE  LEAD  AND  OF  THE  COPPER  GROUP 


Lead  and  Tin 

Lead.  —  Lead  is  a  metal  with  a  bluish  tinge.  It  is  soft, 
being  easily  cut  with  a  knife.  It  is  heavier  than  iron,  its 
specific  gravity  being  11.3,  but  it  is  far  from  being  the 
heaviest  metal,  notwithstanding  the  phrase  "heavy  as 
lead."  The  heavier  metals  are,  however,  not  so  common, 
gold,  for  instance,  being  seldom  seen  in  large  quantity. 
Lead  melts  easily,  and  the  metal  can  be  readily  hammered 
and  bent.  It  is  therefore  useful  for  making  water  pipes 
and  is  largely  employed  in  plumbing. 

There  are  two  important  oxides  of  lead.  One  of  them, 
litharge,  whose  composition  is  shown  by  the  formula  PbO, 
is  employed  in  the  preparation  of  boiled  linseed  oil  and 
also  in  the  making  of  lead  glass.  In  lead  glass,  lead 
oxide  is  used  instead  of  lime  :  the  glass  is  heavy  and  very 
brilliant,  and  is  used  in  cut  glass.  Red  lead,  or  minium, 
PbgO^,  is  more  valuable  for  making  lead  glass,  because 
the  excess  of  oxygen  is  useful  in  getting  rid  of  impurities 
in  the  materials.  Red  lead  is  also  a  valuable  pigment. 
By  far  the  most  important  pigment  is  white  lead,  a 
mixture  of  car])onate  and  hydroxide  of  lead.  The  best 
quality  is  made  by  a  slow  process.  Many  attempts  have 
been  made  to  invent  a  more  rapid  process  and  so  to  pro- 
duce the  white  lead  at  lower  cost.     The  difficulty  with 

200 


METALS   OF  THE  LEAD  AND   COPPER   GROUPS     267 


GROUP 


It  is  soft, 
n  iron,  its 
being  the 
heavy  as 
common, 
quantity, 
lammered 
iter  pipes 

of  them, 
ula  PbO, 
i  oil  and 
lass,  lead 
and  very 

minium, 
,  because 
npurities 
pigment. 
!  lead,  a 
The  best 
pts  have 
►  to  pro- 
ilty  with 


the  white  lead  made  by  most,  if  not  all,  of  the  rapid 
methods,  is  that  it  is  not  so  opaque  and  has  not  so  good 
a  covering  power  as  that  made  by  the  older  and  slower 
process.  Many  substances,  such  as  zinc  white  (an  oxide 
of  zinc),  and  barytes  (barium  sulphate),  have  been  put 
upon  tlie  market,  but  they  are  inferior  in  these  respects 
to  white  lead,  which  is,  however,  open  to  the  objection 
that  it  is  poisonous. 

Lead  is  chiefly  obtained  from  the  sulphide  galena,  com- 
monly found  as  a  deposit  in  limestone.  Tlie  sulphur 
is  burned  off,  the  process  being  somewhat  complicated, 
because  oxygen  not  only  removes  part  of  the  sulphur, 
but  also  oxidises  some  of  the  lead  to  oxide,  while  some 
of  the  lead  sulphide  is  changed  to  sulphate.  At  the  end 
of  the  process,  however,  metallic  lead  is  obtained.  Galena 
very  frequently  contains  silver,  and  the  greater  part  of 
the  silver  in  the  market  is  obtained  from  argentiferous 
(silver-bearing)  galena.  The  silver  is  obtained  with  the 
lead.  One  process  of  separating  silver  from  lead  is  to 
melt  the  argentiferous  lead  and  allow  it  to  cool.  Nearly 
pure  lead  crystallises  out  just  as  nearly  pure  ice  is  formed 
when  salt  water  is  frozen,  and  the  solid  lead  is  removed, 
leaving  a  lead  very  rich  in  silver.  When  this  lead  is 
lieated  in  air  it  oxidises,  forming  the  oxide  litharge.  The 
operation  is  carried  on  in  a  cupels  a  dish  ma«le  of  bone-ash. 
The  litharge  is  partly  volatilised  and  is  partly  absorbed 
by  the  cupel.  The  silver  does  not  oxidise,  and  so  is  left 
pure.  It  is  difficult  to  entirely  free  lead  from  silver,  and 
hence  perfectly  pure  lead  is  more  expensive  than  lead 
containing  a  small  amount  of  silver. 

Tin.  —  Tin  belongs  to  the  same  group  of  elements  as 
lead.     It  is  a  white  metal  and  does  not  tarnish  readily  in 


268 


CHEMISTRY 


the  air.  It  is  therefore  used  as  a  covering  for  iron,  tin 
plate  being  slieet  iron  covered  with  a  coating  of  tin.  A 
bar  of  tin  when  bent  gives  a  peculiar  sound,  called  the 
"tin-cry,"  due  to  friction  of  the  crystals  upon  each  other. 
Tin  forms  useful  alloys ;  gun  metal  and  bronze  are  alloys 
of  copper  and  tin,  and  tin  amalgam  is  used  for  coating 
the  backs  of  mirrors.  The  only  important  ore  of  tin  is 
tinstone,  the  dioxide  SnOg.  The  oxygen  is  readily  re- 
moved by  heating  the  ore  with  anthracite. 

SnOg  +  2  C  =  Sn  +  2  CO. 

Various  salts  of  tin  are  valuable  mordants. 


CoppEK,  Silver,  Gold 

Copper,  silver,  and  gold  are  metals  which  have  some 
similarities  and  form  a  group.  They  all  form  compounds 
in  Avhich  they  act  as  univalent  elements ;  for  instance, 
there  are  the  chlorides  CuCl,  AgCl,  and  AuCl.  But  the 
more  common  chloride  of  copper  has  the  formula  CuClg, 
and  of  gold  the  formula  AuClg. 

Copper.  —  Copper  is  the  most  easily  oxidised  of  the 
three  metals,  being  oxidised  by  heating  in  the  air ;  silver 
and  gold  cannot  be  oxidised  directly  by  oxygen,  and  the 
oxides  when  produced  are  easily  decomposed  by  heat 
alone. 

Experiment  110.  Into  a  test-tube  (preferably  of  hard 
glass)  put  a  mixture  of  copper  oxide  and  charcoal  powder 
and  fit  up  as  shown  in  Fig.  90.  Heat  and  pass  the  gas 
into  lime-water. 

Copper  oxide  readily  gives  up  oxygen  when  heated 
with  carbon,  carbon  dioxide  and  copper  being  produced. 

2CuO-hC  =  2Cu4-  00^. 


METALS  OF  THE  LEAD  AND  COPPER  GROUPS 


269 


Y  iron,  tin 
)f  tin.  A 
called  the 
ach  other, 
are  alloys 
3r  coating 
5  of  tin  is 
eadily  re- 


lave  some 

ompounds 

instance, 

But  the 

ila  CuClj, 

}d   of  the 

ir;  silver 

I,  and  the 

by   heat 

[y  of  hard 
il  powder 
s  the  gas 

n  lieated 
produced. 


An  oxide  such  as  zinc  oxide  or  tin  oxide,  which  is  less 
readily  reduced,  requires  a  higher  temperature,  and  carbon 
monoxide  is  produced  instead  of  carbon  dioxide. 

ZnO  +  C  =  Zn  +  CO. 

All  three  metals  —  copper,  silver,  and  gold  —  are  found 
native,  but  copper  is  also  found  as  a  sulphide,  frequently 
with  iron,  as  in  copper 
pyrites  CuFeSg.  Silver 
is  also  found  as  sulphide, 
mainly  in  galena.  Gold 
occurs  almost  always  in 
the  metallic  state,  contain- 
ing, however,  other  metals 
alloyed  with  it.  The  ex- 
traction of  copper  from 
copper  pyrites  depends 
upon  the  fact  that  iron  is 
more  easily  oxidised  than 
copper,  which  holds  more 
firmly  to  the  sulphur.   The 

pyrites  is  roasted  and  the  roasted  mass  is  heated  with 
silica,  which  combines  with  the  oxide  of  iron,  forming  a 
slag  and  allowing  the  copper  sulphide  to  collect.  Finally, 
the  copper  sulphide  is  oxidised  by  roasting,  thus  removing 
the  sulphur  and  leaving  the  copper. 

CuS+  Oj  =  2  Cu  +  aS'Oj. 

The  copper  is  in  a  somewhat  impure  state.  Copper  is 
used  for  electrical  purposes,  being  a  very  good  conductor, 
nearly  as  good  as  silver,  which  is,  of  course,  too  expensive 
to  be  employed  in  this  way.     Slight  impurities  in  copper 


Fig.  90 


270 


CHEMISTRY 


diminish  its  conductivity  very  much,  and  hence  very  pure 
copper  is  necessary.  Nearly  all  of  the  pure  copper  of 
commerce  is  now  obtained  by  electrolysis.  An  impure 
copper  is  arranged  to  form  the  positive  pole  or  anode,  in 
a  solution  of  copper  sulphate,  and  Avhen  the  current  of 
electricity  i^  passed  through  the  solution,  pure  copper  is 
deposited  on  the  negative  pole  or  cathode.  The  copper 
of  the  positive  pole  goes  into  solution  and  the  impurities 
are  left  behind. 

Copper  is  a  red  metal ;  it  is  soft  and  tough,  malleable 
and  ductile.  Its  alloys  with  tin  have  been  already  men- 
tioned ;  with  zinc  it  forms  brass. 

Silver.  —  The  method  by  which  silver  is  obtained  from 
argentiferous  galena  has  been  already  described.  Silver 
is  a  white  metal,  mainly  used  for  coinage,  for  tableware 
such  as  forks  and  spoons,  and  for  jewellery.  The  principal 
use  of  silver  salts  is  in  photography.  Many  silver  salts 
are  affected  by  the  light.  If  to  a  solution  of  silver 
nitrate  a  chloride  is  added,  silver  chloride  is  produced 
as  a  white,  curdy  precipitate,  but  on  standing  for  some 
time  in  the  light  it  becomes  dark.  Many  silver  salts  are 
affected  by  light,  and  ordinary  photographic  plates  con- 
tain compounds  which  are  very  sensitive.  Light  produces 
an  effect  on  the  plate,  which,  however,  cannot  be  detected 
till  the  plate  is  developed.  In  the  process  of  developing, 
the  silver  compounds  in  the  part  of  the  plate  which  has 
been  exposed  to  a  strong  light  are  darkened  and  rendered 
insoluble  in  certain  liquids  that  dissolve  the  unaffected 
silver  salts,  while  the  parts  of  the  plate  less  exposed  are 
less  darkened.  In  this  way  the  lights  and  shades  of  the 
object  photographed  are  reproduced  and  a  likeness  is 
obtained. 


METALS  OF  THE  LEAD  AND   COPPER  GROUPS        271 


3  very  pure 
copper  of 
\n  impure 
r  anode,  in 
current  of 
B  copper  is 
rhe  copper 
impurities 

,  malleable 
•eady  men- 

lined  from 
id.  Silver 
tableware 
e  principal 
silver  salts 
of  silver 
produced 
'  for  some 
r  salts  are 
>lates  con- 
t  produces 
e  detected 
eveloping, 
which  has 
I  rendered 
unaffected 
:posed  are 
des  of  the 
ikeness   is 


Gold. — Gold  is  found  in  the  gravel  of  some  streams, 
and  is  separated  by  washing  away  the  ligliter  material, 
leaving  the  gold.  It  is  also  found  in  quartz  veins,  from 
which  it  is  usually  extracted  by  crushing  the  ore  and 
bringing  it  into  contact  with  mercury,  Avhich  forms  an 
amalgam  with  the  gold,  from  which  the  mercury  is  after- 
wards driven  off  by  heat.  The  gold  is  usually  not  all 
extracted  by  this  method,  but  the  other  proces'jfos  of 
extracting  it  are  too  complicated  to  be  described  here. 
Gold  is  one  of  the  heaviest  metals.  It  is  the  most  mal- 
leable of  metals,  and  can  be  beaten  into  sheets  so  thin 
as  to  be  transparent,  being  very  much  thinner  than  the 
thinnest  tissue  paper.  Though  the  metal  is  yellow,  light 
shows  greenish  through  the  thin  sheets.  Gold  is  valuable 
chiefly  because  it  does  not  tarnish,  and  the  supply  is  so 
limited  that  its  possession  indicates  wealth.  Because  its 
value  fluctuates  so  little,  it  is  the  standard  medium  of 
exchange,  and  paper  and  silver  money  have  their  value 
because  they  represent  a  certain  amount  of  gold. 


m' 


*^<<W»*|lUliil»|l»llilll 


APPENDIX 


THE  THERMOMETER 


The  thermometer  is  a  measurer  of  temperature.  The  only 
kind  necessary  to  describe  here  is  the  mercury  thermometer,  in 
which  temperature  is  measured  by  the  expansion  of  mercury. 

A  capillary  tube,  together  with  a  bulb  blown  at  one  end,  is 
filled  with  mercury  at  such  a  temperature  that  when  cooled 
it  will  fill  thf!  bulb  and  a  small  piece  of  the  stem.  The  tube  is 
then  closed. 

In  order  to  graduate  the  tube,  the  thermometer  is  placed  in 
melting  ice,  the  position  of  the  mercury  marked,  the  ther- 
mometer being  then  placed  in  the  vapour  of  boiling  water, 
and  the  position  of  the  mercury  again  marked.  These  two 
fixed  points  enable  the  thermometer  to  be  graduated. 

There  are  two  thermometric  scales  in  which  the  melting 
point  of  ice  is  taken  as  the  zero.  These  are  the  Centigrade 
and  Reaumur  scales.  In  the  former  the  boiling  point  of  water 
is  called  lOO  (whence  the  name  centigrade) ;  in  the  latter,  80. 

In  the  Fahrenheit  scale  the  distance  between  the  melting 
point  of  ice  and  the  boiling  point  of  water  is  divided  into  180 
parts.  The  melting  of  ice  is,  however,  not  the  zero,  but  is 
called  32°,  and  the  zero  probably  marks  what  Fahrenheit  con- 
sidered the  lowest  attainable  temperature. 

The  method  of  changing  from  one  scale  to  the  other  is  so 

clearly  given  in  Tait's  "  Heat "  that  I  transcribe  it.     "  If  we 

suppose  the  same  thermometer  to  have  these  three  separate 

scales  adjusted  to  it  or  (still  becter)  engraved  side  by  side 

T  273 


274 


APPENDIX 


upon  the  tube,  we  easily  see  how  to  reduce  from  one  scale  to 
the  other. 


F-f- 


.12 


12 


i!L 


M. 


"For  if  /,  c,  r  be  the  various  readings  of  one  temperature,  it 
is  obvious  that 

/-  32  bears  the  same  ratio  to  (212  -  32  or)  180 
that  c  bears  to  100 

and  r  bears  to  80 

/-32^    c    ^  r  V 
180        100     80' 


"  Hence 


m^ 


one  scale  to 


2I12 


i|»a 


80. 


iperature,  it 

180 

100 

80 


INDEX 


Acetylene,  207. 
Acid,  33. 

arsenic,  188. 

hydriodic,  123. 

hydrobroniic,  12.3. 

hydrochloric,  04,  89. 

hypophosphorous,  178,  182. 

nitric,  127. 

oxalic,  57. 

phosphoric,  ^79. 
meta-,  181. 
ortho-,  180. 
pyro-,  181. 

phosphorous,  182. 

sulphuric,  167. 
Acids,  -ous,  163,  166,  227. 

dibasic,  172,  180. 

tribasic,  180. 
Air,  44,  75. 

liquid,  45. 
Alkali  metals,  2.32. 
Alkaline,  15. 

earths,  247. 
Allotropic,  36. 
Alloys,  231. 
Aluminium,  264. 
Amalgams,  255. 
Ammonia,  46,  191. 
Ammonium,  244. 

amalgam,  245. 
Amorphous,  155. 
Analysis,  24,  171. 
Anhydride,  135. 


Anode,  11. 
Antimony,  189. 
Argon,  43. 
Arsenic,  184. 

pentoxide,  188. 

trioxide,  185. 
Arseniuretted  hydrogen,  187. 
Arsinc,  187,  191. 
Atom,  75. 
Atomic  theory,  72,  75. 

weight,  82. 
Avogadro's  Law,  78. 

Barium.  247. 
Bessemer  converter,  262. 
Bismuth,  191. 
Blast  lamp,  224. 
Bleachhig,  38,  110,  165. 
Bonds,  213. 
Bone-ash,  182,  267. 
Bone-black,  196. 
Boron,  226. 
Brass,  270. 
Bromine,  115. 
Bronze,  268. 
Burette,  6Q. 

Cadmium,  252. 
Caesium,  246. 
Calcium,  247. 
carbide,  207. 
Calculation,  105. 
Carbon,  193. 


275 


2T() 


INDEX 


Carbon,  bisulpbido,  118. 

dioxide,  r»4,  01. 

monoxide,  64,  02. 
Cathoilo,  11. 
(Muu'coal,  \\y.\. 
Cldorato,  121. 
Chlorine,  107. 
Chlorine  peroxide,  125. 
Choke-damp,  207. 
Chromium,  205. 
Coal,  201. 
Cobalt,  20.3. 
Combu.stion,  slow,  203. 
Compound,  11. 

.stable,  110. 
Condy's  fluid,  2. 
Constitution,  251. 
Copper,  2(58. 

Corrosive  sublimate,  254. 
Crucible-,  11)1). 
Cupel,  207. 
Cui)rio  nitrate,  147. 

Decrepitation,  155. 

Delinite  proportions,  Law  of,  74. 

Deflagrating  spoon,  31. 

Diamond,  200. 

Dibasic,  172,  180. 

Dimorphous,  154. 

Dissociation,  50. 

Distillation,  destructive,  40,  202. 

Double  decomposition,  99. 

Effervescence,  54. 

Electrolysis,  11,  03,  239,  241,  242, 

253. 
Electropositive,  230. 
Element,  11. 
Empyreumatic,  104. 
Endothermic,  223. 


E<iuations,  102. 
E(iuivalent,  70. 
Ethylene,  211. 
Eudiometer,  44,  52. 
Exothermic,  223. 
Experimental  error,  73. 

Ferric  chloride,  202. 
Ferrous  chloride,  202. 
Filtrate,  17. 
Fire-dump,  200. 
Flame,  214. 

oxidising  and  reducing,  220. 
Fluorine,  120. 
Flux,  257. 

Fornnda,  81,  114,  200. 
Furnace,  blast,  257. 

puddling,  200. 

reverberatory,  200. 

Gaseous  volume.  Law  of,  78. 
Gases,  kinetic  theory,  84. 

solubility  of,  35. 
Gay-Lussac's  Law,  78. 
Gennan  silver,  265. 
Glass,  244,  200. 
Gold,  208,  271. 
Graphite,  199. 
Gun  metal,  208. 
Gunpowder,  243. 

Halogens,  107,  123. 
Heat,  latent,  (5. 
Hematite,  24. 
Hydrate,  230. 
Hydrocarbon,  211. 
Hydrogen,  9,  12. 

combustion  of,  23. 

antimonide,  190. 

arsenide,  187. 

peroxide,  38. 


INDEX 


277 


Ilydropjcn,  phosphide,  170. 

sulphide,  157. 
Hydroxide,  230. 
Hydroxy  1,  230. 
llypoclilorites,  123. 
llypophosphite,  178. 

Ignition  temperature,  ol. 
Iodine,  110. 
Iron,  26(5. 

cast,  250. 

pig,  250. 

wrought,  250. 

galvanised,  255. 

ores  of,  250. 
Tsoniorpljisni,  251. 

Kindling  temperature,  51. 
Kinetic  tlieory,  84. 

Lampblack,  108. 
Latent  heat,  0, 
Laughing  gas,  141. 
Lead,  200. 

nitrate,  150. 
Liebig's  condenser,  3. 
Lime  light,  225. 
Lime-water,  54,  240. 
Lithium,  240. 
Lixiviation,  235. 

Magnesium,  252,  253. 
Manganese,  204. 
dioxide,  30,  03. 
Marsh  gas,  205. 
Marsh's  test,  180.         ' 
Matches,  125,  183. 
Mercuric  oxide,  20,  92. 
Mercury,  252. 
Metals,  227. 
Methane,  203. 


Mixture,  11. 

Molecule,  70. 

Mordant,  205. 

Multiple  proportion,  Law  of,  74. 

Nascent  hydrogen,  187. 
Neutral  point,  ()8. 
Nickel,  2(i3. 
Nitrates,  127. 
Nitric  anhydride,  135. 

oxide,  14.">. 
Nitrites,  148. 
Nitrogen,  30,  127,  101. 

peroxide,  150. 

trioxide,  148. 
Non-metals.  227. 

Organic  chemistry,  203. 
Oxide,  JK). 
Oxygen,  0,  28. 
Oxyhydrogen  blowpipe,  225. 
Ozone,  30. 

Paris  green,  188. 
Phosphates,  180,  182. 
Phosphine,  178. 
Phosphorus,  173. 

red,  175. 

yellow,  175. 
Photography,  270. 
Platinised  asbestos,  109. 
Potash,  caustic,  70,  243. 
Potassium,  12,  242. 

carbonate,  243. 

chlorate,  20,  124,  174. 

permanganate,  2,  203,  204. 
Precipitate,  54. 

Quicklime,  01,  240. 

Radical,  compound,  128. 
salt,  128. 


278 


INDEX 


Red  precipitate,  20. 
Reducing  agent,  160,  165,  182. 
Replacement,  117. 
Residue,  66. 
Rubidium,  246. 

Safety  lamp,  218. 
Sal  to,  85. 

acid  and  neutral,  101. 
Silicon,  226. 
Silver,  268,  270. 
Slag,  257. 
Soap,  244. 
Soda,  caustic,  66,  238. 

water,  50. 
Sodium,  12,  05,  232. 

bicarbonate,  240. 

carbonate,  234. 

sulphate,  233. 
Solubility  of  gases,  36. 
Solution  in  water,  6. 
Spiegeleisen,  262, 
Steel,  261. 
Stibine,  191. 
Strontium,  24 <. 
Sublimation,  122,  189. 
Substitution,  117. 
Suffix,  -ate,  127. 

-ic,  138. 

-ide,  96. 

-ite,  148. 

-ous,  138,  148. 
Sulphates,  100. 


Sulphides,  156. 
Sulphite,  106,  167. 
Sulphur,  152. 

flowers  of,  and  roll,  156. 

dioxide,  162. 

trioxide,  169. 

varieties  of,  157. 
Sulphuretted  hydrogen,  157. 
Superphosphate,  180. 
Symbols,  76,  80. 
Synthesis,  24,  171. 

Tempering,  262. 
Thermometer,  7. 
Tin,  266,  267. 
Tribasic,  180. 
Type  metal,  189. 

Valency,  98,  213. 
Vitriol,  blue,  4. 

green,  18. 

oil  of.  18. 

white,  25. 

Water,  decomposition  of,  12,  16. 
distillation  of,  2. 
electrolysis  of,  8. 
freezing  of,  1. 
hardness  of,  250. 
solution  in,  0. 

Zinc,  262. 


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